Abstract: This paper describes the study of very long wavelength infrared(VLWIR, c14 m) HgCdTe detectors, used for the remote atmosphere sounding. The very long wavelength band is particularly rich in information about humidity and CO2 levels and provides additional information about cloud structure and temperature distribution across the atmosphere. According to the results, it is shown that the VLWIR HgCdTe detectors have abnormal current-voltage phenomenon at a low temperature, which may be the results of a parasite pn junction. Besides, through data analysis and curves fitting, it is shown that the surface current of the VLWIR HgCdTe diodes is nearly comparable with the bulk current, which reflects that the surface effect is large in the VLWIR HgCdTe diodes. Through the results, it proves that the passivation of diodes is very important.