Abstract: A process for preparing methylene bis-(dialkylamino-dithioformate) in one step includes: simultaneously feeding all or part of four raw materials: dialkylamine, an aqueous solution of sodium hydroxide, dichloromethane and carbon disulfide through a constant-flow pump into a continuous flow reactor; performing the reactions in the continuous flow reactor under a temperature of 10 to 100° C. and with a residence time of 10 to 100 s; simply separating of the obtained reaction products to give the final product. The process synthesizes the product in one step by using the continuous flow reactor. The rapid mass transfer and heat transfer in the continuous flow reactor promote the main reaction, reduce side reactions, improve the product color, and shorten the operation time. Moreover, the yield is relatively high and the quality of the final product meets the requirements.