The method of single channel control is often used in spinning missile. This paper expatiates on the
causation of the periodical mean force, and gives specific ways to get the direction and the magnitude of the force. This paper also introduces the current linear method for controlling the spinning missile. By changing the difference of the linear signal and the control signal into the corresponding phase difference, the effect produced by phase difference is analysed. This paper gets the conclusion: the magnitude and the direction of the periodical mean force are both affected by the phase difference, and the period is , furthermore, this paper gives out the precise changing rule, the maximum bias angle of the period mean force is 8.8 degrees, and the maximum amplitude of the period mean force is 3 times of the zero phase difference condition, which is important theoretical basis for controlling the missile better.