Based on the theories of random process and reliability engineering, the treatment procedure of test data and the evaluation indices of reliability for vehicle products were analyzed. A method of model identification for failure distributions law of entire vehicle was proposed subsequently. In addition, how to determine the life-span of complex repairable system by using random process model was also introduced. Through analyzing a set of test data for a medium truck, it draws a conclusion that both the first failure mileage and the failure interval mileage are subjected to Weibull distribution. Finally, the expressions of reliability function and the evaluation values of reliability indices for this medium truck are listed.