The invention provides a solid-state reference electrode and a preparation method thereof. The solid-state electrode is applicable to oxidation-reduction potential measurement of an all-vanadium flow battery electrolyte; the solid-state reference electrode comprises a silver plate, a silver sulfate membrane, an ion exchange membrane, a lead and an electrode housing; the silver sulfate membrane coats the silver plate; the silver sulfate membrane and the silver plate form a reference electrode body; the reference electrode body is put into the electrode housing; one end of the reference electrode body is connected with the lead, and is used for exporting oxidation-reduction potential measurement data of the all-vanadium flow battery electrolyte; and the other end of the reference electrode body is connected with the ion exchange membrane, and is used for measuring the oxidation-reduction potential of the all-vanadium flow battery electrolyte. Therefore, the solid-state reference electrode is conveniently arranged in an engineering flow pile pipeline system; the potential of the electrode is stable for a long period of time; and in-situ online monitoring of the ORP potential is achieved.