Photolithography is a very critical process in the fabrication of HgCdTe infrared detector chips. At present, most HgCdTe chips are prepared by using contact-lithography technology. However, the process uniformity is poor when exposing chips with large surface undulations, and the mask is easy to damage the chips when contacting with the chips. Aiming at these shortcomings of contact-lithography, a stepper projection exposure process for HgCdTe chips is developed using the reduced-stepper projection lithography machine produced by Nikon. Both hardware and software of the device are slightly modified and set up to work with HgCdTe chips. After debugging, the reduced-stepper projection lithography machine has achieved better exposure effects on some chips with large surface undulations, and the consistency of lithography patterns has been improved. The experimental results show that the reduced-stepper projection lithography technology can improve the lithography quality of HgCdTe chips, and improve the chip preparation process to a certain extent.