The invention relates to a preparation method for a gas sensor for detecting hydrogen, wherein, ultrasonic wave and low-temperature aging technologies are applied in the complex effect of zinc salts and stannum salts and chemical coprecipitation for preparation of nano ZnSnO3. The invention prepares the novel PdO-ZnSnO3 heater type semiconductor gas sensor by isomerisation of noble metal salts PdCl2, adhesives (ethyl orthosilicate) and deionized water through technologies like grinding, ultrasonic vibration, coating, sintering, etc. on the basis of the nano ZnSnO3, wherein, nano ZnSnO3 bases are prepared by adoption of an improved coprecipitation method. The preparation method for the gas sensor for detecting hydrogen has the advantages of high sensitivity of gas sensitive materials, strong selectivity, low operation temperature, simple preparation technology and so on.