Satellite antenna is a key component for satellite communications. In order to ensure the reliability of antenna deployment mechanism in orbit, its mechanical properties must be tested on the ground. To achieve this goal, this paper presents a mechanical performance testing system of antenna deployable mechanism which is in multidimensional framework style. The deployment process of antenna under high or low temperature and weightless environment of space can be simulated, and a loading test during the process could be carried on. The scheme and working principle of the testing system has been illustrated, as well as the innovative design of the three degrees of freedom mechanical arm and the loading mechanism. In addition, the mathematical model of the loading system has been built and simulated. Analyses show that the error of gravity balance is less than 2% FS (Full Scale) and error of the loading moment is less than 2%, thus the system can meet the test requirements of deployable mechanism. The testing system has made it a reality that the test of deployable mechanism has stepped from theoretical simulation stage across to the full-physical simulation stage, which is of great significance to ensure the satellite reliable communications in orbit.