The invention provides a process for producing sodium thiosulfate. The process includes steps of adding sodium carbonate into a dissolving kettle, adding water into the dissolving kettle and primarily stirring the sodium carbonate and the water to obtain materials; heating the primarily stirred materials and secondarily stirring the materials; filling the dissolving kettle with sulfur dioxide gas after the materials are secondarily stirred, and slowly stirring the materials; filling the slowly stirred materials with nitrogen to dispel gas; transferring the materials into a reaction kettle after the gas is dispelled, inputting sulfur dioxide gas into the reaction kettle and filling the reaction kettle with the sulfur dioxide gas; adding sulfur into the reaction kettle and carrying out boiling reaction; cooling the reacted materials, filtering the materials and concentrating and crystallizing filtered liquid.