A provided servo loop decoupling method of a four-axle inertial stabilization platform system comprises the following steps: 1, obtaining the angular velocity components at Xp axis, Yp axis and Zp axis according to the angular velocity of a gyroscope installed on a platform body; 2, measuring and obtaining the internal relative rotation angle and angular velocity of the four-axle inertial stabilization platform system; and 3, calculating the synthetic rotation angular velocity of the platform body, an internal frame, an outer frame and a servo frame. The method is capable realizing servo loop decoupling calculation without singular value under the circumstance that the platform system relative rotation angle is an optional value, thereby improving the full attitude adaptation capability of a carrier under the condition of no trajectory constraint.