The invention relates to a method and a device for detecting and setting a default value of a nuclear power plant digital control system. The method comprises the following steps of: detecting a network fault signal which is received by a non-safe level digital meter control platform, and setting the corresponding default value to be 0; detecting a hard wire signal, and after determining that the hard wire signal is an ineffective signal, setting the default value corresponding to the hard wire signal; and detecting a sensor signal, and after determining that the sensor signal is the ineffective signal, setting the default value corresponding to the sensor signal. The network signal, the hard wire signal and the sensor signal are subjected to classification detection and default value setting on the basis of a safe level digital meter control platform and the non-safe level digital meter control platform of the nuclear power plant digital control system, and the default value is set by combining the nuclear safe particularity of the nuclear-power industry, so that the signal judgment and the parameter setting work of the default value are convenient and optimized.