Chemical sensing film is the key component of surface acoustic wave(SAW)gas sensor.In this pa- per,the absorbing principle of film material for chemical vapor and the theoretical calculation for the re- sponse of SAW gas sensor are described;and the progress of research on chemical sensing films is summa- rized,including polymers,supermolecules,inorganic materials,molecule liquid crystals and biological films.The future development of film materials is forecasted.