Estimating combustion timing in diesel engine by cylinder head vibration acceleration was presented. The correlation between the vibration acceleration and the second derivative pressure was compared based on a 195 diesel engine finite element model. Results showed that the vibration acceleration and the second derivative pressure had the similar trend before the peak pressure, and the combustion timing was supposed to be identified by the zero vibration acceleration at this range. Experiments were conducted on a 195 diesel engine and the results verified that the combustion timing could be determined by the vibration acceleration of cylinder head with the deviation within ±1.5°CA.