The invention belongs to the technical field of industries, and especially relates to a method for detecting switch-on pulse width precision of automatic and protection equipment. The method is applied to developing regular inspection and checking work on an automatic device and relay protection equipment. The method comprises a test computer, a local control unit LCU, an end distribution board, and a relay protection or safety automatic device; the test computer 1 is connected with one end of the local control unit LCU, the other end of the LCU is connected with the end distribution board, and the other end of the end distribution board is connected with the relay protection or safety automatic device. The equipment purchasing and maintenance cost of the equipment is reduced while the measurement precision is guaranteed, the field checking working efficiency and the economy are improved; and meanwhile, the wiring way is simple, the checked equipment is free from power-on and like operations, and the malfunction behavior is avoided. The method further has the advantages of being simple in wiring, less in workload, capable of directly comparing a detection result, and convenient toevaluate the quality of the device switch-on pulse width.