The stable circuit is the important component of the platform inertial navigation system, with the function of isolating the angular motion of the airplane. Its precision and reliability affect directly the precision and reliability of the inertial navigation system. According to the fault analysis, the outer ring bearing, DC torque motor, slip ring and control circle are the main parts of stable circuit. On the basis of deducing the dynamic stiffness of the stable circuit, the failure mechanism is analyzed and the relevant solution is presented. These measures have been applied in the inertial navigation systems. The fault analysis shows that, after taking the solution, the fault rate of the stable circuit decreases greatly and these solutions are effective.