Seven common optical methods for gas concentration detection are described. The basic principles, advantages and disadvantages of each method are given in detail. The improvement work and some novel ide-as are presented. The applications of combined methods are discussed. These optical methods include some conventional gas concentration detection technologies, such as optical interferential method, photoacoustic de-tection (PAS), correlation spectroscopy, and some novel gas concentration detection technologies, such as tuna-ble diode laser absorption spectroscopy (TDLAS), evanescent wave field sensing technology, hollow core pho-tonic bandgap fiber (HC-PBF) sensing technology and fiber loop ring-down spectroscopy (FLRDS). The prospect of optical gas sensing is listed at the end of the paper, which mainly refers to miniaturization, intelligence, porta-bility, low power consumption, high accuracy, fast response and distributed multi-component telemetry technolo-gy.