Hydraulic-pneumatic brake system is one of the most typical one in heavy truck and very heavy truck. Their character is combined hydaulic drive with pneumatic drive, therefore, studying dynamics of hydraulic-pneumatic drive in vehicle brake system is complicated and invovle huge calculations. Using "Simulation with concentrated parameters" method with Simulink to study process that happen in hydraulic-pneumatic drive in vehicle brake system not only reduce amount of calculations but also lead to acceptable result. From the research, the author could determine period of gas load process, brake - delay time, etc..or study system structure parameters effect on dynamics of the system, that are important meaning in university teaching and studying in Vietnam.