The invention relates to a terminal posture error compensation method for a decoupling mechanism based on an inertia force in a trace tracking test. The terminal posture error compensation method comprises the following steps: forming a compensation database relevant with motion errors of an air vehicle model; carrying out an air vehicle model motion test by virtue of the decoupling mechanism, so as to obtain a posture of the air vehicle model and the accelerated speed magnitude on each shaft; searching the motion errors of the air vehicle model from the compensation database according to the posture of the air vehicle model and the accelerated speed magnitude on each shaft; searching a to-be-compensated compensation amount of the air vehicle model from the compensation database according to the motion errors of the air vehicle model; and compensating the motion errors of the air vehicle model according to the compensation amount. According to the terminal posture error compensation method for the decoupling mechanism based on the inertia force in the trace tracking test, a posture error of the air vehicle model can be compensated in real time, so that the posture precision of the air vehicle model is improved.