The traditional no-damp equation of a engine-mount system was modified with consideration of gyro effect. To indicate the effect of gyro moment on the mount system, including frequency domain response and time domain response, the new system was analyzed. The engine-mount was optimized for the traditional equation and the new equation, respectively, using the genetic algorithm. The results for two equations were analyzed and compared, which showed that the gyro effect of the crankshaft system could be ignored for low rotating-speed engine and it should be considered for higher rotating-speed engine.