We investigate the device properties of In_0.53Ga_0.47As/InP avalanche photodiodes (APDs) with different multiplication layer thicknesses of 1.5, 1.0 and 0.8 μm by the Zinc diffusion method. The punch-through voltage and the breakdown voltage increase with the increase of the multiplication layer thickness. On the basis of the simulation by the Silvaco software, the influences of the multiplication layer thickness on the electric field, current-voltage characteristics, breakdown voltages and punch-through voltages are studied. As the multiplication layer thickness increases, the electric field intensity decreases, in contrast, both of the punch-through and breakdown voltages increase,which are consistent with the experimental results. A further study shows that when the multiplication layer thickness is smaller than 0.8 μm and as the multiplication layer thickness increases, the breakdown voltage first decreases and then increases, while the punch-through voltage monotonically increases.