Single-photon detectors for the near-infrared wavelength region are receiving widespread attention in an increasing number of photon counting applications. In fields such as quantum information processing, quantum communication, 3-D laser ranging (LiDAR), time-resolved spectroscopy, etc. An InGaAs/InP single photon avalanche diode (SPAD) was designed and demonstrated to detect 1 550 nm wavelength photons in this paper. The SPAD has a separate absorption, grading, charge and multiplication region structure (SAGCM) with single photon sensitivity when working in Geiger-mode. The characterization of the SPAD include breakdown voltage, dark count rate, single photon detection efficiency and after pulse probability as functions of temperature from 223 to 293 K. The 25 μm diameter SPAD shows certain temperature dependency, with breakdown voltage dependence of approximately 100 mV/K. Operating at 223 K and in Geiger-mode, the SPAD achieves a photon detection efficiency of 21% at 1 550 nm with a dark count rate of 4.1 kHz and a after pulse probability of 3.29%. The source and physical mechanism of the photon detection efficiency, dark count rate and after pulse probability of the SPAD with temperature dependency were also analyzed and discussed. The mechanism analysis, discussion and calculation can provide more theoretical basis and support for the design and fabrication of SPAD.