This study focused on the effects of tooth manufacturing errors (MEs) on the dynamic behaviors of a helical geared system. The composite mesh error is introduced and calculated, which is taken as error excitation in the dynamic model. A combined finite element method (FEM) and analytical contact model is used to investigate the interaction of mesh stiffness and MEs. The dynamic model is developed based on the finite element method and its effectiveness has been verified. By introducing stiffness excitation and error excitation, the effects of mesh stiffness and MEs can be easily distinguished in the total excitation. The influence degrees of these two factors are obtained at different torque levels by simulating the quasi-static and dynamic responses of the system. The results show that the composite mesh error will have great changes under light load conditions, and larger dynamic factors as well as decreased resonance speed will be brought. The excitation produced by manufacturing errors is dominate in the total vibration excitation in a light loading, while the excitation produced by mesh stiffness is becoming the dominating one in a heavy loading. [ABSTRACT FROM AUTHOR]