Abstract:Based on the features of network economy and the theory and practice of antimonopoly law, the author proposes the impacts of static characteristics, dynamic characteristics of network economy and trade form in network space on the definition of relevant marketFurthermore,the author reveals that the market share is not a key factor to define dominant position in network economy The key factors are network economic effects, standard and intellectual property of the key facilityFinally,the suggestions for legislation are given by analyzing relevant articles of Anti monopoly Law of People’s Republic of China