For making the layout of production line more reasonable, it is an effective method to use computer simulation. This paper takes a ball valve production line of K company as research object, first each process time was measured in the method of stopwatch time study, then production line models were established by using Flexsim software. After that, simulation of original production line and the optimized one was carried out. The results show that using Flexsim simulation can improve production line balancing rate, capacity and average work rate of all processes.