The invention provides a method for preparing a proton-conducting film, the proton-conducting film produced by the method and a solid polymer type fuel cell using the proton-conducting film. The proton-conducting film has a cross-linking structure with silica covalent bonds and is provided with a cross-linking structure containing sulfoacid in the film represented by the following formula (1). The method is characterized in that the method comprises the following steps: the first step is to prepare a mixture containing sulphydryl oligomer (A) which is provided with a plurality of sulphydryls and reactive groups which can form Si-O-Si bonds through condensation reactions; the second step is to form the mixture into a film; the third step is that the film modal mixture forms cross-linked gel by the condensation reaction involving catalyst; and the fourth step is that the sulphydryls in the film is transferred into sulfoacid groups through oxidation. The proton-conducting film representshigher ionic conductivity, has excellent dimensional stability at high temperature, and can operate stably even at high temperature.