A way of gas detection on the basis of gas infrared absorption which produces thermal effects is presented.A kind of infrared capacitive gas sensors have been designed and manufactured.The gas sensor seals pure test gas in sealed chamber.Pure test gas absorbs infrare producing thermal effects which leads to pressure change.This pressure change transform into elastic film strain resulting in capacitance variation.As a result of difference absorption of infrared between seals pure test gas in sealed chamber and mixed test gas in environment

the capacitance variation express test gas concentration change in environment.The experimental result show that methane detection lower limit is 100×10-6 while its resolution can reach 50×10-6.