The photovoltaic mid-wave infrared HgCdTe detector, which is operated at room temperature, is simulated to explore laser irradiation saturation characteristics. The results reveal that the heating effect on the HgCdTe material and the lowering of the zero-bias impedance due to irradiation, are significant factors affecting the quantum efficiency of the detector. The model of HgCdTe pn junction is established, and a one-dimensional numerical simulation method is adopted to compute the quantum efficiency and zero-bias impedance of device. The device is irradiated under steady-state. Moreover, the temperature field distribution is coupled in the simulation, the thickness of substrate affects the temperature of the detector, which significantly affects the saturation threshold of the device. Furthermore, the calculations show that the zero-bias impedance of device decreases when the light intensity is raised. The result is compared to the measured performance of device. Finally, the computational analysis serves as a foundation for the development of mid-wave IR HgCdTe detectors with high saturation irradiance threshold.