This paper takes the rate gyroscope as the research object and expounds on the importance of the built-in test function of the rate gyroscope. Starting from the composition and working principle of the liquid-floated rate gyroscope, the cross-linking and built-in test architecture of the flight control system and the rate gyroscope are explained, and the built-in test process is clarified. Based on the built-in test architecture and built-in test mechanism, combined with the working principle of the gyroscope, a mathematical model of built-in test is established. According to the built-in test output requirements of the flight control system for the rate gyroscope, a built-in test design method is proposed, which aims to determine the nominal values and error ranges of key parameters (torque coefficient, built-in test winding resistance) through analysis. This design method has been applied to multiple types of liquid-floated rate gyroscopes and can effectively identify product failures during field use.