The present invention is directed to a client-server network system implementing a multi-tier caching strategy for a user to access a document efficiently. The system comprises a client cache assistant serving as proxy for web browsers, a remote cache server managing user-requested documents and a search engine repository storing a huge number of documents as a backup for the remote cache server. Upon receipt of a document request, the client cache assistant examines its client cache to identify the requested document. If not successful, the remote cache server then identifies a copy of the requested document in its own cache and transmits a content difference between the two copies to the client cache assistant. If the server copy is still not fresh or not found, the remote cache server seeks another copy of the requested document from the search engine repository and transmits another content difference to the client cache assistant. The client cache assistant merges the content differences and the original copy into a new copy of the requested document.