The HgCdTe infrared detector chip with p-on-n structure has low dark current and long lifetime. It is the mainstream development direction of the high-performance infrared detector. In order to meet the development requirement of miniaturization of the future infrared detector, the p-on-n long-wave 1280×1024 detector with 10 μm pixel pitch was studied. In response to the difficulties of As ion implantation activation and long-wave small-pitch chip preparation technology, research and analysis have been conducted on As ion implantation technology and As activation annealing technology. The optimal conditions were verified by different characterization methods, and the detector chip was prepared through device technology. The I-V characteristic curve was tested, and a detector chip with good performance was obtained. This study is of great significance for the preparation of small-pitch long-wave p-on-n cadmium telluride mercury focal plane devices.