The invention belongs to the technical field of diesel engines, and provides a protection method for controlling full-open pressure reduction by a diesel engine exhaust back pressure test. In the provided protection method for controlling full-open pressure reduction by using a diesel engine exhaust back pressure test, a diesel engine exhaust back pressure main sensor and a diesel engine exhaust back pressure spare sensor are arranged in a corresponding diesel engine exhaust pipeline; the diesel engine exhaust back pressure main sensor and the diesel engine exhaust back pressure spare sensor are communicated with a monitoring unit in a diesel engine exhaust back pressure regulation control device respectively to form an automatic control monitoring unit; the input-output control module ofa control unit is communicated with an electric regulating valve for controlling the regulation of the electric regulating valve; an emergency full-open control button is further arranged in the diesel engine exhaust back pressure regulation control device; and the emergency full-open control button is respectively communicated with the monitoring unit and the electric regulating valve in the diesel engine exhaust back pressure regulation control device. According to the protection method, under a fault condition or an emergency condition, the full-open pressure reduction can be effectively controlled through diesel engine exhaust back pressure.