Abstract: Aiming at the problem about that the abnormal noise appears at the engine front end in the idle and accelerated states,which usually happens in initial design and development stage,the near field noise measurements on full engine test bench are conducted.Through the frequency calculation of different sections of accessory belt and the diagnostic analysis of noise spectrum,it can be seen that the main factor of generating idle noise is the effect of the tension of accessory belt.Moreover,both the resonance noise generated by thin-walled structure and the order noise generated by timing chain system in the accelerated state can be reduced after improving the structural dynamic stiffness of the engine timing cover and performing the optimal design of the timing chain respectively.The experimental results show that there are three main ways to control the abnormal noise at engine front end:the tension of the accessory belt,the dynamic stiffness of the shell structure surface of timing cover and the vibration impact of the timing chain system.