Based on the methane spectral absorption characteristic and second harmonic detection technology

a method of detecting methane concentration is presented.Taking distributed feedback(DFB) laser as the light source

using the sinusoidal signal to modulate the light frequency DFB laser

the light through an gas cell which is filled with methane and nitrogen is detected by a optoelectric detector.The methane concentration is obtained after dealing with the signal by using the technology of second harmonic detection

and the experimental results accord with the actual methane concentration.At last

the factors influencing on the experimental detecting resolution are analyzed.This research shows that the technology can realize the complete non-contact automatic detection on line

and can satisfy the need of methane safe detection in coal mine.