Photoconductive effect and heat effect in semiconductor photoconductive detectors when they are irradiated by laser were considered simultaneously. A transportation model of photoconductive carriers and heat transmission model were established. The photoconductive carriers consistency and the heat equilibrium carriers consistency in PC-type HgCdTe detectors under various laser irradiation density were calculated. Instantaneous change behaviors of the detectors were imitated further. The imitative results arsults are identical with experimental results.