The incorporation behaviour of arsenic and phosphorus in the GaAsP teary alloy under phosphorus-rich conditions is studied based on the incorporation coeffcient model and the growth diffusion model combined with the alloy composition data obtained by high resolution x-ray diffraction analysis.It is found that As adatoms have longer surface lifetime and longer migration length than those of P adatoms, which leads to an arsenic incorporation efficiency much higher than that of phosphorous.With the increase of arsenic flux, the surface lifetime of arsenic adatoms decreases due to the competition of As adatoms.The detailed analysis and discussion are given here.