The dimension synthesis of crank rocker mechanism used in torque exciter was carried out with known angular displacement of rocker swing. Optimization method based on minimum kinetic energy of whole mechanism was adopted under constraint condition of minimum transmission angle and mechanism bar existence condition. Optimization design function was applied in solution and a design method of crank rocker mechanism was developed. The torque exciter has been in operation, achieving scheduled function for dynamic performance test, and all testing data are exact and valid.