The invention relates to engineering machine speed changing box power cut-off control, aims at overcoming the defect that when an existing speed changing box power output cut-off control system cuts off power output or recovers power output, impacts can be generated, and discloses an engineering machine speed changing box power output cut-off control system and method. According to the braking pressure, the joint degree of a power cut-off clutch in a speed changing box is controlled; when the braking pressure value is smaller than P1, the joint degree of the power cut-off clutch is 100%; whenthe braking pressure value ranges from P1 to P2, the joint degree of the power cut-off clutch ranges from 0% to 100% and is reduced along with increasing of the braking pressure value; and when the braking pressure value is larger than P2, the joint degree of the power cut-off clutch is 0%. The slope control principle is used in the engineering machine speed changing box power output cut-off control system and method for controlling the power output of the speed changing box, disengaging and engaging of the power cut-off clutch are gradually changed, power cut-off and recovery are stable, theimpacts are reduced, the service life of power components is prolonged, and the work comfort is improved.