Arsenic-doped long-wavelength HgCdTe was realized by ion implantation. As doping medium,arsenic shows amphiprotic doping property. When Arsenic only occupies Te-site to be acceptor,P type HgdTe material can be formed. After the arsenic-doped HgCdTe is annealed in the mercury atmosphere,the change of electrical property which is caused by annealing is analyzed. And the effect of mercury pressure,temperature and time on arsenic activation is studied. The activation effect is analyzed by Hall measurement and SIMS. In the end,when the arsenic-doped HgCdTe is annealed in the high temperature and high mercury atmosphere,arsenic activation is achieved.