Abstract: In actual practices, a soft-start trip of constant-speed oil pump may result in the inconsistency between remote-control and on-site running states and the delayed restart. In order to solve this problem, a new method to control the running state of constant-speed oil pump in the case of soft-start trip was developed with reference to the electrical equipment control theories and the PLC program logic. By virtue of this method, the auxiliary start/stop state signals of existing soft-start equipments at all stations along Mohe-Daqing Crude Oil Pipeline are uploaded to the station control PLC system. Then, the fault state of soft-start trip is diagnosed by using the control logic programmed in the station control PLC system so as to control the high-voltage circuit breaker of constant-speed pump unit. In this way, the high-voltage circuit breaker can be separated in time once a soft-start trip occurs, so that the remote-control and on-site running states of pump unit remain consistent and the delayed restart will not occur after a soft-start trip. When this method is used, no more hardware is needed, so the cost is saved. By means of this method, the potential safety hazard caused by the soft-start trip of constant-speed oil pump unit is eliminated effectively.