Wavelength modulation technique (WMT) and wavelength sweep technique (WST) are introduced into intra-cavity absorption gas sensors (ICAGS) for low concentration gas detection. The optimized parameters of the system maximizing the signal-to-noise ratio (SNR) are found. Calibration of acetylene concentration and gas recognition are both realized. Wavelength modulation technique (WMT) and wavelength sweep technique (WST) are introduced into intra-cavity absorption gas sensors (ICAGS) for low concentration gas detection. The optimized parameters of the system maximizing the signal-to-noise ratio Calibration of acetylene concentration and gas recognition are both realized.