大家都知道外部链接对SEO的重要性，这一点毋庸置疑，尤其是优化热门关键词时。很多人疑惑更多的是，什么样的外部链接才是好的链接？
下面从比较理想化的情况看看好的外部链接应该具备哪些条件。
链接网站与你的网站有没有内容相关性
如果对方网站内容和你的网站内容相差十万八千里，就算在首页上给你个链接，对你的排名也帮助不大。当然如果对方PR值很高，带给你的好处是你的网站PR值也会相应提高。但要注意Google工具条显示的PR值不是真实PR值，与排名也没有直接关系。
如果你的目的是想提高相关关键词的排名，那还是找相关网站的链接。
链接页的排名怎么样
对方能给你链接的那个网页，在搜索你的目标关键词时，排在什么地方？排名越好，说明这个特定网页在搜索特定关键词时价值越高，给出的链接对你的网页排名影响也越大。
如果是商业性的关键词，排在前面的很可能是你的竞争对手的首页，想从那里得到链接可能性不大。但是你可以把目光放到前一百名，甚至两百名。这些网页在搜索引擎眼里针对特定关键词的权重也都不若，虽然用户一般都看不到。在前一两百个网页中，经常会有大量非商业网站，非竞争对手的网页。
链接网址整体排名怎么样
看一下对方网站的目标关键词是什么，搜索一下这些关键词，看看这个网站整体排名如何。同样，这里并不要求一定是排前二十名，只要能在前一两百名就不错。网站整体排名体现了这个域名在搜索引擎眼里的权重。
能给你的锚文字是什么
当然最好是你所希望的目标关键词。如果锚文字是“点击这里”之类的，效果就大打折扣。
强调一遍，链接锚文字是相当相当重要的。
链接的位置
网页正文中的链接效果最好。如果链接是放在导航部分，或者通常是放赞助商链接的地方，搜索引擎可以判别出来这不是内容的一部分。当链接是在文章正文中时，才最有可能是文章作者给出的一个投票。
网站整体健康情况
这包括Google PR（我知道，Google PR很多人已经不看重，与排名也没有直接关系，但查一下总比不查好），搜狗Rank，域名注册时间，是否在DMOZ中有收录，网站整体有多少个外部链接。这些健康状况检查，都有助于确保链接网站的权重。
链接页有多少个导入链接
这包括内部链接和外部链接。
如果对方网站本身权重很高，但给你链接的那个页是特意为友情链接而做，对方网页很少链接到这个友情链接页，那么这个链接页所获得的权重就大大降低。
如果链接页是正常内容页，除了获得的内部链接和其它网页一样，如果内容好的话，也很可能会有大量外部链接，数量越多越好，可以用雅虎查一下反向链接。
链接页上导出链接数目
这一点相信大家都知道，特定页上导出链接越多，每个链接所带的权重就被分散了。如果只是几个导出链接，那么你得到的权重份额也相应提高。
Alexa排名
很多时候外部链接并不仅仅带来链接权重，还能带来真实的点击流量。所以看一下对方的Alexa排名也是必要的。当然应该注意看曲线是自然增长曲线，还是明显作弊得到的。
如果上面列出的都能拿高分，那这是外部链接中的极品了，可遇而不可求。
译文:
What kind of external links are good links?
We all know the importance of external links to SEO, which is undoubted. Especially when optimizing popular keywords, all that people doubt more is what kind of external links are good links.
Below from the comparatively idealized situation to see which conditions are required by good external links?
Whether the relevance of content exists between link website and your website or not
If the content of opposite website is totally different from that of your website, even though link with your website at home page, it is not very helpful for your ranking. Certainly, in case that the PR value of opposite website is quite high, then the advantage led to you is that the PR value of your website will be correspondingly increased, whereas what we shall pay attention to is that the PR value showed on Google Toolbars is not real and it has no direct relationship with ranking.
If you just target at the improvement of ranking of relevant keywords, you'd better look for some connected website links.
How about the ranking of link page
Where is the website linked by opposite party when searching your targeted keywords? The higher ranking is, the higher value of such a particular website in search of specific keywords is, the greater influence of given link on you website ranking is.
In case of the commercial keywords, the top websites may belong to your competitors, so it is impossible to link with them. However, you can keep your eyes on top one hundred, even two hundred. For search engines, weights of these websites aiming at the specific keywords are all heavy, although users cannot see them commonly. Among such top one hundred or two hundred websites, there is often a large number of non-commercial and non-competitive website.
How about the overall ranking of link website
To see the targeted keywords of opposite website, then search these keywords to see the overall ranking of this website. Similarly, top twenty is not required here, just top one hundred or two hundred is enough. The overall ranking of website reflects the weight of such a domain name in the eyes of search engines.
What is your given link text
Surely the best is the targeted keywords you hope. If the link text is something like “click here”, effects may be significantly reduced.
So mention one more time, link text is quite important.
Place of link
Link in the text of web page makes the best effect. If in hub page or commonly in the place of sponsored links, search engines can judge that it is not a part of content. If in the text, it is most possible for article to vote.
Overall condition of website health
It involves Google PR (I know, Goggle PR, rarely valued by many people, has no direct deal with ranking, but it is better to have a look.), Sogou Rank, date of domain registration, whether DMOZ is included or not, how many external links the website totally possesses. Examinations of such health condition benefit the guarantee of link website's weight.
How many back links exist in link pages
Internal links and external links are included.
If weight of opposite website is very heavy, while the link page given to you is jut for friendship link, opposite web page seldom link this friendship link page, and then weight gained by the link page will be greatly reduced.
If link page is normal content page, the same as other web pages except the acquired internal links, in case of good content, there may be lots of external links, the more, the better, and Yahoo can be used to search back links.
Number of back links in link page
As you all know, with the increasing number of back links in particular pages, weight carried by each link will be separated. If only several back links, your weight will be correspondingly increased.
Alexa Ranking
Many times, external links not only bring about the link weight, but also the actual traffic volume, so it becomes necessary to see Alexa ranking of opposite party, and moreover, attention should be paid to curve to prove that it is the naturally cumulative curve or acquired by cheat.
On condition of achieving high marks in the aspects listed above, such external links are best of all that only come out by accident.