Why it will make a great difference for the keywords' Rank when I search it with Google and some other Seo Tools in Google Search Engines sometimes?
Sorry that no one has replied to this, as it's actually an interesting question. Sometimes when you use rank-checking tools you hit a different Google datacenter, and ranking results vary across the datacenter.
Phillip is right! Different search engines have diffrent algorithms. So your main focus should be satisfying the major search engines first then the smaller ones if necessary.