The study on As 4-doped HgCdTe epilayers grown by MBE was presented. The electrical activation of arsenic impurities was achieved by annealing that caused As to occupy Te sites. By using the secondary ion mass spectrometry (SIMS) and Hall measurements on the in situ arsenic doped HgCdTe epilayers, the results show that P-type MBE HgCdTe can be obtained by doping with As 4 source and annealing with high temperature.