According to kinetic analysis, we put forward a braking control strategy under the down shift condition. When auxiliary engine brake torque affects the stability of vehicle, it should disconnect the clutch; and when auxiliary engine brake torque doesn’t affect the stability of vehicle, it should jointing the clutch. The speed acceleration, the braking time, and the braking distance are analyzed in while the clutch and joint the clutch are disconnect. The analysis indicates that when auxiliary engine brake torque doesn’t affect the stability of vehicle, jointing the clutch can reduce the braking time and distance obviously.