HgCdTep-on-n structure infrared detector has low dark current and long lifetime, which is the main development direction of high-performance infrared detectors at present. Meanwhile, in order to meet the development needs of future infrared detector miniaturization, this paper mainly studies p-on-n long-wave 10 micron pixel spacing 1280×1024 detector. The p-on-n heterojunction technical route was adopted to study the forming and passivation technology of the small-pitch mesa. The mesa and passivation morphology were evaluated by SEM, the quality of the passivation layer was evaluated by CV test, and the detector was developed. The I-V characteristics of the pn junction of the detector were evaluated by a semiconductor parameter tester at 77K, and the IV characteristic was tested. The performance of the detector is tested by the test of the performance, and the detector with good performance is obtained. This study is of great significance for the preparation of small-pitch long-wave p-on-n infrared detector devices.