The failure modes of the timing system are classified,the internal factors and the external environment factors are distinguished in detail. Combining the failure summary of failure of 78 kits of failure timing system,the parts with the highest frequency failure mode,the main causes of failure and the most common failure result are given. It is determined that the tensioner and the chain are the components with highest failure frequency in the timing system,and the abnormal sound is the most common consequence of the failure of the timing system.