In order to detect weak light in telecommunication wavelength, InGaAs/InP single-photon avalanche diode (SPAD) is receiving increasing interest. The operation conditions which contains excess bias and operating temperature will effectively influence the performance of SPAD. After analyzing the structure of SPAD, the integrated model of intrinsic parameters of SPAD including photon detection efficiency (PDE) and dark count rate (DCR) is built, which is based on the excess bias and operating temperature. Moreover, the integrated model is compared with the measured data, and it is verified to be able to predict the PDE and DCR accurately. Then, combining with the bit error rate (BER) model of photon-counting based optical wireless communication, the optimal operation conditions of SPAD are investigated. The simulation results show that with the increasing of excess bias from 0-V to 10-V, BER can be effectively reduced. And keeping the excess bias at 5-V can make the BER reach its bottom, when excess bias is limited by the gating circuits of f5-V. In addition, cooling the SPAD to operate at around 245-K could let the system work at the optimal BER.