To nonlinear model of guided projectile with some uncertain and unknown aerodynamic parameters, a controller was designed by combining the backstepping with immersion and invariance (I&I).First, a manifold that denotes the parameter estimation error was set up，then its invariance and attractiveness were maintained by the input of controller and parameter adaptive rate so that the estimation error will converge to zero on this manifold．It was not necessary for the parameter estimator to obey the certainty-equivalence principle.Finally, the stability of the closed-loop control system of the projectile was verified by Lyapunov stability theory.The simulation result shows that the proposed control system can accomplish the trajectory control of the angle of attack under the condition of uncertainty of aerodynamic parameters.