Abstract: The factors are studied which lead to a disturbance of abnormal frequency added into the gyro-output signal during the control section flight of the rocket in some special conditions, when the spinning rocket is of high length to diameter ratio. Numerical simulation and theoretical analysis were used. The results show that this kind of disturbance is caused by the coupling between the control system and the flexible bending of the rocket body. Occurrance of coupling is evidently related to the magnitude of initial disturbance and the inherent frequency of rocket body. This kind of coupling generally happens in the later stage of the control section flight of the rocket. The frequency of the disturbance in the output signals of gyro is equal to the sum of the frequency of rocket rotation and the first rank inherent frequency of the rocket body.