To optimize the dark current characteristic and detection efficiency of the 1550 nm weak light signal at room temperature, this work proposes a Ge-on-Si avalanche photodiode (APD) in Geiger mode, which could operate at 300 K. This lateral separate absorption charge multiplication APD shows a low breakdown voltage (V_br) in Geiger mode of -7.42V and low dark current of 0.096 nA at unity gain voltage (V_Gain=1 = -7.03 V). Combined with an RF amplifier module and counter, the detection system demonstrates a low dark count rate (DCR) of 1.1×106counts per second and high detection efficiency η of 7.8% for 1550 nm weak coherent pulse detection at 300 K. The APD reported in this work weakens the dependence of the weak optical signal recognition on the low environment temperature and makes single-chip integration of the single-photon level detection system possible.