In the paper, in order to probe the relation between numerical simulation of aerodynamic effect of lateral impulse jet control and time integration scheme, the 2D general jet flow is simulated with unsteady time integration approach, the unsteady aerodynamic characteristics of missile is acquired. The analyse of result shows that lateral impulse jet flow is greatly unsteady and residual influence. Unsteady integration approach should be used when predict aerodynamic effect of lateral impulse jet which chamber pressure is very sharp with time, the result would be better than that of steady integration approach.