The passively quenched operation of avalanche photodiode (APD) has been used to characterizing InGaAs/InP APD including punch through voltage, avalanche voltage and break down voltage that are all important in the design of APD for single photon detection. The punch through voltage at certain doping level can be related to the thickness of the InP multiplication layer and the thickness of the un-intentionally doped n-type InP layer can be adjusted in according to the experimental data. The analysis indicates that the punch through voltage should be close to the breakdown voltage that can be realized by adjusting the thickness of InP multiplication layer.