High quality substrate thinning process is developed for InAs/GaSb type-II superlattice infrared detectors to obtain high quality substrate surface and improve the quality of superlattice infrared detectors. A combination of mechanical polishing and mechanochemical polishing is used to thin the substrate, in which mechanical polishing reduces most of the thickness of the substrate, and then mechanical damage is removed through mechanochemical polishing. In the process of mechanochemical polishing, the influence of the pH value of the mechanochemical polishing solution on the surface quality of the substrate is mainly studied while the pressure, speed, and other factors remain unchanged. The experiment shows that when the pH value of the mechanochemical polishing solution is 94, a high-quality and low damage substrate surface is obtained, and the imaging effect of the detector component is the best.