A low noise InGaAs/InP single photon avalanche diode (SPAD) is demonstrated. The device is based on planar type separate absorption, grading, charge and multiplication structure. Relying on reasonably designed device structure and low-damage Zn diffusion technology, excellent low-noise performance is achieved. Due to its importance, the physical mechanism of dark count is analyzed through performance characterization at different temperatures. The device can achieve 20% single photon detection efficiency and 320 Hz dark count rate (DCR) with a low after pulsing probability of 0.57% at 233 K.