In order to investigate the blade torque fluctuation mechanism and provide more insight into torque converter’s internal flow field, this paper established both single-blade passage and full-blade passage transient simulation model. The time dependent blade torque results from single blade-passage simulation method is actually the torque of those blades which pass through the chosen blade passage range, which can be of great help to analysis the influence of the blade position on the torque pulsation results; while the blade torque from full-blade passage simulation method is actually the torque results of a chosen blade at different time, which can be used to analysis the time dependent result of the blade torque and its frequency results. Thus, the blade torque fluctuation was analyzed by a comprehensive study on transient time-dependent result and the blade space position relationship. The results indicated that the rotor-stator interaction between the stator-pump/turbine- stator, and the rotor-rotor interaction between the pumpturbine were inevitable in the torque converter. The study reveals that the relative blade position between pump and turbine with regard to stator would successively switch time by time, eventually leading to a blade torque fluctuation. Since the position of each blade in an impeller is different, a damping effect would occur when the blade torque is integrated to synthesize the impeller torque, consequently leading to a much smoother wheel torque characteristics.