We have change our main server 3 weak ago. Now we find that our mostly site ranking have fall down at google. Please let me know that is server IP is it reason, I means I want to know that is server IP is also effects on our site ranking.
It depends whether your new IP address resolves to the same location (country) as the old one. Have you made any other changes?
Do a small search on this forum for similar topics, there are PLENTY of threads on this topic already.
I have read in some blog that websites in the same IP (Example: site X (111.222.333.***) and site Y (111.222.333.*** , too), won't exchange pagerank)
IP has nothing to do with pagerank, although links from other websites on the same IP or even c-class range may be devalued for serps reasons. It's generally accepted that changing ip's or hosts won't make a difference in serps unless, like mentioned earlier, the server is located in a different geographical area - example: switching from a UK to a US server, as Google takes into consideration where your located when determining relevancy.