External disturbance is transferred from the base to gyro room through the suspension tape of pendulous gyroscope.In order to analyze the transfer rule of the external moment of suspension tape,a model for the swing angle of suspension tape is established by Lagranges equation based on the structure of pendulous gyro north finder,and is solved under the condition that instantaneous impact force,constant external force and simple harmonic external force are acted on the base.The swing angle of suspension tape reflects the moment of external force borne by gyro room when the angle is small.It is proved by experiment that:1) under certain conditions,frequency of the swing angle of suspension tape approaches to that of a simple pendulum;2) under the instantaneous impact force and constant force,the swing angel of suspension tape becomes to simple harmonic vibration from the moment of being stressed,of which,the swing amplitude depends on the external force;and 3) under a simple harmonic external force,the swing angle of suspension tape is a linear superposition of vibration by both the frequency of simple pendulum and external force,and resonance appears when the frequency of simple harmonic external force approaches to the inherent frequency of simple pendulum.