The invention provides a lubricating oil replacing device for a nuclear power plant. The lubricating oil replacing device comprises an automatic oil pump, an oil pumping pipe, an oil supplying pipe, an oil inlet pipe, an oil outlet pipe and an oil storage tank for storing lubricating oil. The oil pumping pipe is provided with a first valve, the oil supplying pipe is provided with a second valve, the oil inlet pipe is provided with a third valve, and the oil outlet pipe is provided with a fourth valve. The oil storage tank is provided with an oil inlet and an oil outlet, one end of the oil outlet pipe is connected with the oil outlet, both the other end of the oil outlet pipe and one end of the oil pumping pipe are connected with the input end of the automatic oil pump, and the other end of the oil pumping pipe is an oil pumping connecting end. One end of the oil inlet pipe is connected with the oil inlet, both the other end of the oil inlet pipe and one end of the oil supplying pipe are connected with the output end of the automatic oil pump, and the other end of the oil supplying pipe is an oil supplying connecting end. The lubricating oil replacing device for the nuclear power plant has the advantages of being simple and compact in structure, low in manufacturing cost, easy to maintain, free of manual power providing, easy and convenient to operate, capable of saving labor, efficient in lubricating oil replacement, and capable of discharging old lubricating oil in mechanical equipment completely.