The World Wide Web is the largest collection of data today and it continues increasing day by day. A web crawler is a program from the huge downloading of web pages from World Wide Web and this process is called Web crawling. To collect the web pages from www a search engine uses web crawler and the web crawler collects this by web crawling. Due to limitations of network bandwidth, time-consuming and hardware's a Web crawler cannot download all the pages, it is important to select the most important ones as early as possible during the crawling process and avoid downloading and visiting many irrelevant pages. This paper reviews help the researches on web crawling methods used for searching