The semiconductor-passivating layer interface, as well as the dielectric properties of the passivator, plays an important role in HgCdTe based photoelectric detectors. Anodization is commonly used as a surface passivator for HgCdTe. ZnS is deposited on the AOF (anodic-oxide film) as antireflecting layer. The electrical properties of the interface between AOF/ZnS and LWIR bulk HgCdTe materials were determined by capacitance-voltage (C-V) measurements in the frequency range of 10 KHz-10 MHz in the metal insulator semiconductor (MIS) structures. The results showed that the MIS detector could not reach the high frequency level even at frequencies up to 10 MHz in the case where the interfacial state densities were 3.4×1011 cm-2q-1V-1. The fixed charges were 1.1×1012cm-2. The surface recombination velocity at the interface of AOF/ZnS and LWIR HgCdTe was 700cm/s. The variation of C-V properties with temperature has been obtained and analyzed.