As an important part of vehicle following control system, vehicle longitudinal dynamic model had significant effect on the research and development phases. The clutch engaging and exhaust brake process of AMT vehicle represented strong nonlinearity, and the theoretical models were complex and depended on many parameters. Focusing on the requirement of following control system, the models of the two processes above were simplified for the engineering application by combining theoretical analysis and real vehicle test data to describe the dynamic processes. Finally, the vehicle model based on MATLAB was build and the comparative experiments were conducted. The comparative results show that the simulation results agree well with the real vehicle tests.