An adaptive filtering algorithm for laser absorption spectroscopy was investigated. An improved measuring system scheme of laser absorption spectroscopy was proposed. Light beam emitted from laser was divided into three beams which constructed measurement channel, calibration channel and reference channel, respectively. Data acquisition circuit acquired signal data from three channels. Data from calibration channel was used for wavelength locking and concentration calibration. Signal data from reference channel contained noise associated with the measurement channel. Based on this, an adaptive noise canceller was constructed to reduce the effects of noise on measurement channel and improve the accuracy of the gas concentration inversion.