The surface defects of HgCdTe p-on-n double-layer heterojunction materials are studied. The surface defects of materials will affect the performance of subsequent devices. Through observing the surface of the epitaxial material with the optical microscope, it is found that the surface irregular blocky defects and surface hole defects are common. By using confocal microscope, scanning electron microscope, energy spectrum analysis and other testing methods, it is found that the defects originate from the depletion of cadmium in the growth process of p-type layer and the extension of defects in the growth process of n-type layer.