In order to improve the transmission accuracy of the multistage gear transmission system effectively and economically,the transmission accuracy model of the multistage gear drive system based on the theory of error coupling compensation is established. A numerical analysis method is used to calculate the transmission accuracy of the multistage gear transmission system,and the corresponding initial phase of eccentric error is analyzed when the system coupling transmission accuracy is aimed at the minimum transmission accuracy. Then,the system transmission accuracies are both calculated by the Monte Carlo method when it is under the random assembly of the components and it is improved machining accuracy of some parts. Finally,by comparing and analyzing the transmission accuracy under the three situations,the results show that the transmission accuracy of the multistage gear transmission system is improved with the numerical analysis method,which verifies that the method is feasible and valid.