Abstract: The single-pump multi-motor transmission system can provide multiple speeds and torques. In order to make the output torque of the single-pump multi-motor transmission system more stable, the system, which was composed of double-action pump and double-action double-stator motor, was selected as the object of research, the fluctuant factor was adopted to analyze the influence of the fluctuant input oil on the output torque of the motor, and the fluctuant curves of the motor were drawn under 4 different working ways (inside motor working alone, outside motor working alone, inside and outside motor working jointly, and inside and outside motor working differentially). The practical output torque fluctuation of motor was liner superposition between torque fluctuation and input oil fluctuation. Their fluctuant curves were linearly combined with the same method. When the pulsation cycle of input oil was different from output torque's, the sum of them was aperiodical, and the practical output torque fluctuation was irregular. On the contrary, when the pulsation cycle of input oil was identical with output torque's, by adjusting the lag angle between pump and motor, their fluctuant curves could be reasonably stacked, and the motor could practically output the minimum torque fluctuation. To verify the influence of lag angle on the single-pump multi-motor transmission system, a test platform was established, which was composed of double-action pump and double-action double-stator motor. By recording the multi-group measuring instantaneous output torque values, the multiple torque fluctuating coefficients were calculated under each working way of motor and then the fluctuation curves were drawn together. These lines could intuitively reflect output torque fluctuation values under different working ways of motor and compare the different effect on the output torque fluctuation by adjusting lag angle. The results showed that under the premise of input oil fluctuating, the motor had different output characteristics under different ways of working. When the pump fluctuation cycle was consistent with the motor's, the output torque fluctuation under the way of the inside and outside motor working differentially was the minimum, whose torque fluctuating coefficient was about 1.5%-1.8%. The output torque fluctuation under the way of inside motor working alone was always less than the outside motor's. Different lag angles had different effects on the output torque fluctuation of motor. Among the 4 different working ways, the way of inside and outside motor jointly working was most affected by lag angle, whose torque fluctuating coefficient value was up to about 1.9%-2.7%; and its change range was the most, about 0.8%, more than the other 3 working ways. Reasonably adjusting lag angle could make the output torque fluctuation coefficient under this working way decrease to 1.5%-2%, which was less than that under the ways of the inside or outside motor working alone, and the overall change range reduced to about 0.5%. Reasonable lag angle could also make the overall output torque fluctuation of the motor reduced. This experiment indicates that lag angle has a great impact on the output torque fluctuation of the motor. For the transmission of high precision occasions, the research on reasonable lag angle has great significance can provide a theoretical basis for the piping layout of single-pump multi-motor transmission system.