In order to improve the attitude determination accuracy of the guided rocket which transverse size is not enough for fixing multiple antennae, a single-antenna GPS aiding attitude determination method was proposed. The pseudo attitude was introduced, using which the concrete algorithm for obtaining the altitude is analyzed. And the model of the single-antenna GPS aiding attitude is established. The Kalman filtering is adopted to filter the state vector model. And the relative velocity and acceleration is obtained. According to the relationship between ordinary and pseudo attitude, the ordinary attitude of guided rocket is obtained. Throughout the simulation research, the feasibility and effectiveness of the application of single-antenna GPS system on rocket projectiles is demonstrated.