Abstract: Assembly line is a common form of production in manufacturing enterprises, and the efficiency of assembly line directly affects the production of the whole production line. The balance rate of production, the balance loss rate and the smoothness index are used as the parameters to evaluate the production balance, and the basic IE method is used to solve the balance problem in the production line. On the basis of the production line balance principle, the production balance index of A 3 assembly line is calculated on the basis of the actual working hours, and IE method used to analyze and improve the assembly line. To prove the IE method is scientific and effective, Flexsim software is used. After improvement, the production line balance rate increases from 67.24% to 93.89%, the smoothness index decreases from 8.69 to 1.26. Thus it can be seen that the effect of improvement is significant.