The characteristics method was used to solve continuity equation and momentum equation of transient second air system in engine

and the energy equation was solved iteratively.The time-dependent change rules of pressure

mass flow rate and temperature of the flow in second air system were calculated.The result shows that the changes in pressure and mass flow rate of inner nodes vary similarly with the changes of inlet pressure with a corresponding delay time of 0.01s

and the temperatures of elements vary with the boundary temperature.The quasi-static results show good agreement with that of software of Flowmaster

and the maximum relative error of pressure is 0.051%.