Predicting the effective life of relay protection devices accurately is the essential to ensure the safe and stable operation of smart substations. This paper proposes a life prediction method based on cloud model and Markov chain. This method utilizes the operating status data of the relay protection device and combines with the membership function of the cloud model to construct the initial state probability distribution vector. Then the state transition probability matrix is obtained according to the Markov chain principle. Finally, the effective life of the protection device is predicted according to the reliability criterion. The example analysis results show that this method can effectively predict the effective life of the protection device and can also provide guidance for the state maintenance work of the relay protection device in the smart substation. This work is supported by National Natural Science Foundation of China (No. 51277135).