In this note, a class of gun control system of tank is considered with all uncertainties, such as unknown constant parameters, unlinearly parts, unparameterized parts, unmodeled parts, unknown external disturbance and so on. An robust adaptive control law is designed with backstepping technique. Compared to exist results on tank gun control problem , our control scheme combine the robust control and the adaptive estimator of unknown constant parameters and can compensate all uncertainties Accurately. The stability of closed loop system and the tracking performance can be guaranteed by this control law. Simulation studies show that this controller is effective.