The invention belongs to the technical field of industrial automation control, and provides a DCS avalanche condition simulation method and device for a nuclear power plant. The method comprises the steps: S1, exporting an engineering database from a DCS, wherein the values of I/O signals of the I/O variable data points in the engineering database can be changed in the DCS in a manually forced manner, and each data point comprises a plurality of data point items; S2, carrying out the screening of the data points in the engineering database, and obtaining the avalanche test data point items forsimulating the avalanche conditions; S3, storing the avalanche test data points for simulating the avalanche conditions according to a designed format; S4, combining the avalanche test data points, stored according to the designed format, for simulating the avalanche conditions with a timer, importing the data points into the DCS through a DCS interface device, and changing the values of the avalanche test data points in a forced manner, thereby achieving the automatic simulation of the avalanche conditions. Therefore, an independent simulation bottom equipment signal generation device is cancelled in the simulation process of the avalanche conditions, so the test cost is reduced.