Abstract: Suggestions for improvement of U shaped assembly line operation was proposed by a simulation method based on the effective worker behavior model. The influence factors of worker behavior were analyze. On this basis,the fuzzy model of fatigue,failure and work progress was proposed respectively according to the questionnaire results of related workers. The working speed model was proposed by using the fuzzy logic inference theory. This model was applied to a U shaped line simulation,and several suggestions for improvement were proposed according to the simulation results. The optimal improvement plan was chosen by further simulation. The simulation results show that the production efficiency and the task balance rate of U shaped line can be improved effectively by cooperation,changing the work order and working strategy.