Admittance voltage characteristics of Hg 0.66 Cd 0.34 Te CdTe heterostructures were studied by using a wide band admittance measurement system.HgCdTe heterostructures were grown by MBE technology.An energy band structure was established according to the analysis of C V and G V results.It was shown that,holes are accumulated at the HgCdTe surface while depleted at the CdTe surface and the barriers formed at the interface make the carriers confined in HgCdTe.The photovoltaic response spectrum shows two peaks,which are located at 2970cm -1 and 3650cm -1 respectively.The former peak is due to the intrinsic photovoltaic effect of HgCdTe,and the latter peak is due to the effect that holes in the accumulation layer are excited by photons and then overpass the hole barrier at the interface, i.e. ,the hole barrier height is about 0.41eV.