The affects of gamma radiation on the performances of thin film HgCdTe MWIR FPA infrared detector is reparted. The different doses of gamma irradiation is 3 ×10⁶ rad,9×10⁶ rad and 2 × 10⁷ rad. The Ⅰ-Ⅴ characteristics,blackbody responses and noise were measured before and after each dose of irradiation. With the total dose increased,the current and noise of the device increased while blackbody responses decreased. The Ⅰ-Ⅴ characteristics were affected by gamma radiation seriously while blackbody responsively and blackbody responses was affected a little. These shows the performances of the device was degenerated as the dose of gamma irradiation increased.