In order to develop the performance of the transmission system of the engine's valve mechanism and to reduce the resonance invalidation，we defined the quasi-failure resonance state of the transmission system based on the rule that absolute value of difference between the natural frequency of the transmission system and the cam vibration frequency cannot go over the specified threshold. According to the perturbation theory and reliability technology，we derived the expression of the probability of the quasi-failure with normal random variables and put forward the analysis method of reliability to decrease the vibration. Finally, we set the simplified model as an example and calculated the reliability of this system with the proposed method and the Monte Carlo method respectively. Numerical results confirmed that practicability of the proposed method which can avoid the resonance invalidation of valve-train by analyzing the effect of vibration.