The invention provides a molecular weight regulator which comprises the following materials in parts by weight: 1-4 parts of tetrabutyl thiuram disulfide and 1-4 parts of tetraamyl thiuram disulfide. The invention also provides an application of the molecular weight regulator in the preparation of sulfur modified chloroprene rubber. The molecular weight regulator provided by the invention can be added to an oil phase in a proper ratio before emulsion polymerization, so that the molecular weight of a polymer can be effectively regulated and controlled in the emulsion polymerization reaction process, thereby avoiding the chain-breaking process in the existing production method, shortening the time required in the process, lowering the equipment investment and saving the production cost. Besides, chloroprene rubber of an appropriate Mooney viscosity can be prepared, and the Mooney viscosity stability of the product is increased.