Acrylic　acid　(AA)　and　sodium　methallyl　sulfonate　(SMS)　were　grafted　onto　Poly(ethylene-co-tetrafluoroethylene)　(ETFE)　films　by　pre-irradiatic　and　we　prepared　a　humidity　sensing　membrane　including　strong　acid(-SO3Na)　and　weak　acid　(-COOH)groups.　The　structure　and　surface　morphology　both　grafted　and　ungrafted　ETFE　films　are　observed　by　fourier　transform　infrared　spectroscopy　(FTIR)　and　scanning　electron　microscope　(SEM),　respective　A　resistive　humidity　sensor　was　prepared　based　on　the　humidity　sensing　film　and　its　electrical　response　to　humidity　was　examined.　The　films　showed　hi　sensitivity　with　nearly　three　orders　of　magnitude　change　in　the　resistance　during　the　relative　humidity　variation　from　5%　to　98%.The　film　exhibits　sm,　hysteresis(less　than　2%RH)　and　quick　response(abso　ption:　less　than　2　min;　desorption:less　than　4　min).　the　effect　of　grafting　yield　on　humidity　sensi　properties　was　discussed.