Abstract: The dead zone has severely influenced the application of the digital closedloop fiber optic gyroscope (DCFOG) in high performance inertial navigation system. A mathematic model focusing on feedback related interence was established to analyze the dead zone in fiber optic gyroscope and was verified through FOG dead zone measurement of its simulation data by simulink. Based on this,an optical power interference model was proposed, and the frequency characteristic of the interference source analyzed and compared to the optic power affected. Further, an interfer suppressed PCB layout shows a much less coupling and dead zone. All measurement shows that the feedback phase step signal dependent error is the primary cause of the dead zone;besides the electric crosstalk,the phase step dependent modulation of optic power can also bring error to gyro signal processing and cause dead zone. After the targeted design of decoupling and error modulation, the dead band reduces from 0.2/h to 0.02/h, which meets the requirements of the application.