LW HgCdTe thin films were passivated by CdTe/ZnS composite passivation layer, and the growth process of passivation films was improved. The MIS devices and photodiodes were fabricated by using different passivation process. The SEM, C-V and I-V measurement were used to analyze the interface characteristics and its effect on the performance of devices. The results show that the CdTe film grown by improved process is more compact and has no large hole, the lattice structure order degree of CdTe/HgCdTe interface is improved; The C-V curve of MIS device fabricated by improved passivation process reveals high frequency characteristics, and interface fixed charge layers density is decreased from 1.67×1011 cm-2 to 5.69×1010 cm-2. The photodiode with general process has large surface channel leakage current under high reverse bias voltage, whereas the surface leakage current of the device with new process is effectively suppressed.