The CdTe/ZnS double-layer passivation process was used to passivate the surface of the long-wave HgCdTe substrate and optimize the process, and different process conditions were used to grow the backside anti-reflection film. The film layers of the diode devices prepared under various process conditions were characterized by scanning electron microscope (SEM), atomic force microscope (AFM) and I-V curves, and the effect of the density of the CdTe/ZnS film layer deposited under different process conditions on the device performance was studied. The results show that the CdTe/ZnS passivation film layer with higher density is uniform and has a better surface state; the backside anti-reflection film layer with higher density has stronger adhesion and fewer surface defects, and the prepared LW640-15 detector has higher performance.