Servo control is one of the key technologies of the photoelectric stabilized platform. Improving the control rigidity may strengthen the isolation effect, but may result in system instability at the same time. Based on the theory and experiments, the paper builds up the simplified mathematical model of the servo control system, deduces the system control rigidity expression, and points out the method to improve control rigidity. According to Routh stability criterion, the analytic stability condition is solved, which shows the conflict between the stability and control rigidity and that gyroscope is the key factor of the conflict. The results are validated by simulations and experiments, which may provide the reference for engineering application.