Large area n-on-p structures of p-n junction with different proton implantation doses are fabricated on the moleculer beam epitaxial grown HgCdTe films for mid-infrared wavelength region. Current-voltage characteristics of the p-n junction are measured at 77K. The zero-bias resistance-area product (R0A ) of 312.5Ω·cm2 is obtained when the proton implantation dose is 2×10 15cm-2， and R0A increases to 490Ω·cm2 after ann ealing at low temperatures.