The laser simulation method is adopted to study the photocurrent characteristics of N-Metal-Oxide-Semiconductor(NMOS) devices under gamma ray irradiation. The laser experiments are carried out, and the relationship between photocurrent and laser incident energy is obtained for Partial- Depleted Silicon On Insulator(PDSOI) NMOS devices with different sizes and different structures. The photocurrent characteristics of devices are simulated by using TCAD simulation tool. By comparing TCAD simulation and laser experiment data, the results of the two groups of data are basically consistent, which verifies the feasibility and accuracy of the laser simulation technology. The relationship of photocurrent between theoretical calculations and laser experiments is obtained, based on which, the magnification factor of the parasitic bipolar transistor is calculated under the laser condition.