My website is 50 to 60 % similar to other website is this an issue for Google ranking?

[Michael]

my ranking suddenly dropping.

[wilson]

If content is same then it will effect otherwise no chance.

[Jake]

It would certainly be a factor, though it doesn't explain the sudden drop unless you just switched on auto-blog, one phase of the Panda quality filter is sending out a human reviewer, which can results in seemingly unexplainable drops.

If one experiences a sudden drop in search ranking,. it's a good practice to look for a drop in search referral traffic in your server logs that coincides with the date of one of the updates you can find in this calendar of algorithm changes.
http://www.seomoz.org/google-algorithm-change

If trying to get links for the purpose of SEO, it's important to note that some automated methods that worked in the past can now be SEO poison
http://www.seomoz.org/ugc/are-seos-destr...guin-story