A high-speed single-photon detection technique based on gated InGaAs/InP avalanche photodiode (APD) is proposed. The 1.5 GHz harmonics ultrashort pulse is applied to an InGaAs/InP APD, and the photo-excited avalanche signal is buried in the harmonics noise due to the capacitive response of APD. By utilizing a 700 MHz low-pass filter, we achieve 50.6 dB noise suppression and extract the avalanche signal efficiently. With the InGaAs/InP APD operated under -30 ℃ by thermal electrical cooler, and driven by 1.5 GHz harmonics ultarshort pulse gating, a detection efficiency of 35% at 1550 nm with the dark count probability of 6.4×10-5 per gate is obtained, and the afterpulse probability is 6.0×10-5 per gate after 2.7 ns at the detection efficiency of 15%.