Abstract: In order to solve security threats of the system caused by the non-cooperative behavior of individual users in the open cloud environment, a trust model based on "inverted pyramid" classification was proposed. Firstly, the cooperative attitudes of the cloud users were used as a basis for calculating their reputation values. Secondly, the cloud users were managed hierarchically according to their accumulated reputation values. Thirdly, the selection strategies of the users of different levels were judged by complete information static game theory in an interaction process. Simulation results and analysis show that the trust level model can distinguish untrusted users in the system, stimulate cooperative behavior of the users, and improve the ability of system in the prevention of security threats.