Behaviors of As incorporation into HgCdTe in molecular beam epitaxy were studied and reported by using a SIMS(Secondary Ion Mass Spectrometry) quantitative analysis. It was found that the surface sticking coefficient of As was very low, and had a strong correlation with the Hg incorporation. For single crystal HgCdTe epilayers, the sticking coefficient was as low as 3×10 -4 at the growth temperature of 170℃. At this temperature, the good surface morphology of HgCdTe epilayers was obtained by optimization growth conditions, and the As concentration was well controlled by the As oven temperature.