An InGaAs/InP avalanche photodetector (APD）with InGaAsP grade layer and InP charge layer between the InGaAs absorption and InP multiplication region (SAGCM-APD）was simulated.APSYS software was employed for the simulation of energy band,electric field,dark current and current plus response at the wavelength 1.55μm.Results were compared with a sectional charge layer SACM-APD which has the same materials and device thickness.The simulations demonstrated that the heterostructure composed by grade layer and charge layer in SAGCM-APD could make lower leakage current at the lower reverse bias voltage relatively to SACM-APD.A lower punch-through voltage,breakdown voltage and the greater gain also obtained in SAGCM compared to SACM structure.