Air brake system is widely used in heavy duty trucks and buses due to its great performance and efficiency. Dual brake valve (DBV) is one the of major and crucial component of an air brake system as it is controlling the air flow from reservoir to brake chamber during braking operation. Currently, due to its own complexity, it is very difficult for designer to optimize different parameters. As experimentation is tedious and time consuming task, hence it is very important to have mathematical model of DBV during in early design stage. Differential equations have been formulated for individual component of DBV such as primary piston, primary valve, relay piston, and relay valve etc. system level mathematical model has been formulated and implemented in Matlab/Simulink to capture the dynamic pressure characteristic of DBV. At the same time mathematical model of DBV has been created in AMESim to check the validity of approach. Result from these approaches have been verified and validated with experimental results. A comparison of these results shows that adopted approaches have been showing a very good correlation with experimental result. Furthermore same model can be extended to calculate the response time and other characteristic of a complete pneumatic brake circuit.