The invention provides a method used for simulating a device controlled by a nuclear power plant DCS system. The method comprises the steps that the device information is read by a test tool; the current value of a device feedback signal and a device command signal of the simulated device is read in a server; the test tool carries out simulation judging according to current and previous cycle device commands and feedback information; the feedback value of the device after the cycle is acquired, and is written into the server; and communication synchronization with a field control station is carried out, and is used as the device information of a next processing cycle. Compared with the prior art, the method provided by the invention has the advantages that external physical connection is avoided to minimized; a DCS system data interface is used to monitor and change a point value related to each physical device in a real-time database of the system in real time; the external simulation of a physical signal is not needed; a signal is read and written directly through an interface in the system; the device controlled by the nuclear power plant DCS system is simulated; the device cost is greatly reduced; and the efficiency is improved.