The results of indium doping on MBE grown HgCdTe were described.It was found that the indium electrical activation was close to 100% in HgCdTe and the donor activation energy was at least smaller than 0.6meV. It was confirmed that a donor concentration of ～3×10¹⁵cm^-3 was necessarily preserved for infrared FPAs applications. The diffusion behavior of indium was studied by thermal annealing, and a diffusion coefficient of ～10-14cm²/sec at 400℃ was obtained, which confirms the feasibility and validity of indium as an n-type dopant.