The results of n+onp HgCdTe midwavelength infrared detector with a passivation interface is presented. The interface passivation process was optimized using highdensity hydrogen plasma implantation. By implantation barrier layer deposition, ionimplantation window exposure, B+ implantation, passivation film deposition, plasma hydrogenimplantation, metallization and indiumbump arrays fabrication, n+onp HgCdTe midwavelength infrared detector was obtained from a Hg1-xCdxTe film grown by MBE. Cutin voltages of HgCdTe midwavelength detector Photodiodes with interface optimized were 50mV approximately larger than those of the one without optimization. The dynamic resistances at zero bias and reverse bias region were improved 10 times and dynamic resistances at the larger forward region were decreased significantly. Thus, it is obvious that plasma hydrogenimplantation is beneficial to suppress the dark currents and improve the ohmic contact of HgCdTe midwavelength infrared detector photodiodes, and then to enhance the operating dynamic range and performance uniformity.