Web site ranking service is a kind of pay-per-click (PPC) advertising offered by online search engine operators as Baidu.com, which is an efficient method for e-marketing in the network economy era. Besides, it also brings service providers much more profits. However, there are concerns that such Web site ranking service will create a space of commercial fraud and unfair competition, more and more corporations will be kidnapped by this marketing mode because of the market dominant position of Baidu.com in the Chinese search engine service industry. Therefore, lack of legal risk management for the search engine companies in this field has made the Web site ranking service a significant source of disputes. By doing Baidu.com's case study, this article explores the legal problems arising from Web site ranking service, and discusses Baidu.com as an Internet service provider(ISP)- its legal liability under Chinese newly enforced Anti-monopoly Law(AML) mainly. Then, this article tries to analyze other potential legal risks of Internet business under AML as an extensive thought from the discussion beforehand. Finally, this article puts forward some resolutions aiming at protecting the fair and efficient competition environment as well as the rights and interests of all parties. With the hope to achieve three wins, this article presents its conclusion with the suggestion of more clear legislation and other feasible administrative measures.