Abstract: To make up for the lack of researches on E-commerce enterprise monopoly on the internet platform, this paper puts forward a progressive theory and model to measure the monopoly power and structure of E-commerce enterprises on the internet platform around the concentration ratio: the measurement from the perspective of concentration is to define the main body and dimensions of monopoly, the integrality is to measure the monopoly power from the given perspective, the decomposability is to measure the monopoly structure under the given monopoly power, the oligopoly is to measure the oligopoly structure under the given monopoly structure, and the liquidity is to measure the entry barriers under the given monopoly power and structure. The results of the actual measurement on Baidu search engine show that the concentration index of the simple share type, such as Gini coefficient, can better reflect the monopoly power of the E-commerce enterprises on internet platform, that the monopoly power of the E-businesses on the platform is stronger with a Gini coefficient above 0.9, that the monopoly structure forming the monopoly power is mainly made up of the E-businesses in healthcare, education and training, investment joining, and business services, that the monopoly structure has been polarized into a dual structure of oligopoly and catching-up, and that the solidification of the monopoly power and structure makes the entry barrier even harder to break. Through the empirical test, it can be seen that this concentration measurement system (market definition ?monopolistic power ?monopolistic structure ?entry barriers) is a marginal advance on the basis of the existing system (market definition ?monopoly power ?entry barriers), and the empirical results can play a certain role in guiding China’s “Internet +” Action Plan.

Key words: monopoly; concentration ratio; E-business; internet platform