The temperature and magnetic field dependent resistivity was measured for Hg 1 x Cd x Te photoconductive detectors. The density of all kinds of surface electrons was found to keep constant from 1.2K to 55K by the Shubnikov de Haas (SdH) measurements. A three band model, which consists of two kinds of surface electrons and bulk electrons, was proposed to fit the temperature dependent resistivity. The electrical parameters obtained by this model agree well with the experimental data and the results given by SdH measurements.