By using microwave and ultraviolet light irradiation method, when methylthiomethyllithium compound is prepared from dimethyl sulfide, tetramethylethylenediamine is not used, which can not only obtain a high yield but also greatly shorten the reaction time. Experiments show that 2 hours is the best reaction time: the reaction is almost complete and there are almost no by-products. In less than 2 hours, the reaction was incomplete and an excess of 2 hours produced unknown by-products. Dimethyl sulfide is a very weak acid and is very stable under normal conditions. In order to promote the S-H bond rupture, special energy is required. Microwaves and ultraviolet light can increase their energy inside the molecule. The energy of microwave and ultraviolet light increases the fracture tendency of C-Li bond on the one hand, and increases the cleavage of S-H bond in dimethyl sulfide on the other hand, thereby accelerating the reaction process. Experiments show that the ultraviolet light energy is the most important factor in the preparation of methylthiomethyllithium.