For the purpose of analyzing and predicting spin characteristics of aircraft, the rotary balance testing in wind tunnel is mainly used to measure aerodynamic forces acting on aircraft model rotating around the longitudinal axis of wind axes system. In order to meet the demands of project tests and aerodynamic research, the rotary balance system was developed in FD09 low speed wind tunnel. This paper introduces design feature, performance index, and the verification tests using SDM (standard dynamic model) and fighter plane model of the system. The results indicate that the rotary balance system of FD09 wind tunnel is stable and reliable, the repetition of test curves of FD09 wind tunnel and reference curves are good, the test curves of FD09 wind tunnel are more smoothly than reference curves, and the aerodynamic coefficients yielded by the rotary balance system of FD09 wind tunnel have high accuracy. The rotary balance system of FD09 wind tunnel can be put into the project tests and aerodynamic research.