The invention relates to a styrene monomer containing alkyl sodium (potassium) thiosulfate and a preparation method thereof, belonging to the technical field of organic synthesis and high polymer. In the invention, styrene based compound containing halogenated methylene is used as raw materials, methanol or ethanol and water are used as mixed solvent, PEO400 is used as a phase transfer catalyst, the halogen on the halogenated methylene reacts with the Bunte Salts of excessive saturated sodium (potassium) thiosulfate and is stirred to react under the room temperature till the sodium (potassium) thiosulfate raw material is totally consumed, then the methanol or ethanol and part of water are removed from the mixture by pressure reduction, is cooled and crystallized and then carried out the pumping filtration and collection to obtain solid; and the solid is leached (eluted) sequentially by little cooling water and petroleum ether and dried under the temperature of 40 DEG C to obtain the monomer, the monomer releases active sulfhydryl-groups with the function of chain transfer under the action of strong polarity reagents or diluted acid such as DMSO, DMF, and the like to form an AB monomer containing polymerizable double bond as well as active sulfhydral-groups. The AB monomer has simple structure, is easily prepared and stored, and is expected to be applied to super branched polymer prepared by a sulfhydryl-group chain transfer super branched polymerization method.