The long－wave HgCdTe PC detectors were irradiated by laser beam. The power of the laser beam was changeable and below the permanent damnification threshold of the long－wave HgCdTe PC detectors. The resistance－temperature characteristic of the devices before and after the irradiation is measured, since the resistance－temperature characteristic of the devices can be used to study the electric parameters of the material. This method is used to fit the result of the experiment. It indicates that the proportion of the element Cd become larger. It is concluded that the electronic mobility and electronic concentration of the devices would be reduced after the break of the performance of the detectors due to the irradiation of laser beam.