It is a complicated job to determine a reasonable engine mounting system. It must meet a list of static and dynamic performance requirements, and the design is limited by many factors. This paper gives a detailed description of the decoupling arrangement of engine mounting system, and application of center of percussion in the design of mounting system. Taking the improvement on the design of engine mounting system for a truck as an example, by adopting decoupled arrangement, the frequencies of the main vibrational directions of mounting system can be easily controlled, and fall within the desirable range. Meanwhile, decoupling is achieved in the predominant vibrational directions and the isolation of vibration is improved.