The invention relates to a brake auxiliary control method of an automobile AT transmission, which comprises the following steps: calibrating the set automobile speed lower limit value, engine rotation speed upper limit value and loosened accelerator pedal speed value in the TCU of an automobile; respectively analyzing the received loosened accelerator pedal speed signals, engine rotation speed signals, automobile speed signals, shift level position signals and brake signals by the TCU; and when the loosened accelerator pedal speed is greater than the set value, the engine rotation speed is less than the set engine rotation speed upper limit value, the automobile speed is greater than the set automobile speed lower limit value, a shift level is in a non-neutral position and a non-reverse position and a brake is trod down, outputting downshift signals by the TCU to enable the transmission to be in brake auxiliary control. By adopting the method, in the driving process, after a driver urgently loosens the accelerator and treads down a brake pedal, the engine can perform relatively obvious brake auxiliary action on the automobile and can not influence other normal gear shift functionsof the automobile.