Abstract: Near-infrared single-photon detection has attracted much interest for its wide application, especially in quantum teleportation and quantum encryption, which utilize the quantum nature of single photons. Actually, because of their high sensitivity, single-photon detectors can be employed wherever very weak light needs to be measured. The most developed near-infrared detection systems to date are based on the semiconductor avalanche photodiode, the key component. In this paper the parameters of the avalanche photodiode such as dark current and breakdown voltage are described, and the effect and tradeoff relationships between the system parameters including operation temperature, DC bias, gate bias, and threshold are discussed.