The invention provides a synthesis method of a bis-sulfydryl chelating agent for processing heavy metal complex wastewater and particularly provides a synthesis method for 4-methyl-2-mercaptothiophenol. The 4-methyl-2-mercaptothiophenol is the chelating agent and is prepared from the following steps of: carrying out chlorosulfonylation on methyl thiophenol in a proper organic solvent to obtain 5-methyl-2-mercapto-benzenesulfonyl chloride, and carrying out reduction by utilizing a reducing agent, so as to obtain the 4-methyl-2-mercaptothiophenol. A product obtained by utilizing the method is easily separated and is high in yield.