Recently, the quantity of information that is accessible from the Internet is being dramatically increased. Searching the Web for useful information has therefore become increasingly difficult. Thus, much research has been done on web robots which perform internet information filtering based on user interest. If a web site which users want to visit is found, its content is searched by following the searching list or Web sites links in order. This search process takes a long time according as the number of page or site increases so that its performance need to be improved. In order to minimize unnecessary search with web robots, this paper proposes an efficient information collection system based on compare and merge method. In the proposed system, a web robot initially collects information from web sites which users register. From the next visit to the web sites, the web robot compares what it collected with what the web sites have currently. If they are different, the web robot updates what it collected. Only updated web page information is classified according to subject and provided to users so that users can access the updated information quickly.