I have builded many quality inbound link to my site recently, but when I search my site by enterring my site domain, the result has dropped down greatly. Donno why
When you say 'recently', how recently do you mean? It can take a while before the new backlinks are picked up by Google and have an affect on your rankings. In my experience, Yahoo is faster at finding new backlinks. Another possibility is that your competitors are building backlinks faster than you. Mark