The invention provides a low-cost and high-efficiency hydrogen producing method based on a sulfite fuel cell system. The method includes the steps that an ammonium sulfite solution is adopted as electrolyte, a carbon-based electrode is adopted as an anode, a carbon-based electrode or a metal electrode is adopted as a cathode, and electrolysis is carried out; and in obtained electrolysate, an anodeproduct comprises ammonium sulfate, and the cathode product comprises hydrogen. Easy-to-decompose ammonium sulfate within a wide concentration range can be stably treated, and stable sulfur-nitrogenfertilizer, namely ammonium sulfate capable of being used for agricultural production is produced. By means of the reducing capacity of sulfur (IV), additional electric energy needing to be supplied is reduced, and the energy consumption of a hydrogen producing reaction is reduced; and generation of oxygen is restrained, preparation of high-purity hydrogen is achieved, and the dangerousness and the complexity of hydrogen-oxygen separation are avoided. No gas needs to be additionally introduced in the reaction process, the influences of the ambient lighting change are avoided, and the method ismore stable and efficient and higher in operability.