The principle of gas detection with spectrum absorption is explained and the typical gas in coal mine is given. A goaf spontaneous combustion prediction system with multiple parameters is introduced in detail. The system uses a distributed feedback diode laser as light source, which is driven by a low frequency sawtooth wave overlapped with a high-frequency sinusoidal signal. Signal extraction is achieved with a lock-in amplifier. The method to determine spontaneous combustion of coal mine goaf is explained according to the theory of static distribution of three zones. The system uses fiber to detect gas and transmit signal, which makes the real time detection accurate, stable and reliable due to absence of electricity.