The invention discloses a sulfide heavy metal chelating agent N1,N2,N4,N5-tetra(2-sulfydrylethyl)1,2,4,5-pyromellitic formamide and a preparation method thereof. The preparation method of the chelating agent comprises the following steps of: dissolving certain mol ratios of mercaptoethylamine hydrochloride and pyromellitic formic anhydride into dimethylformamide (DMF) at a certain temperature; agitating to react for a period of time and filtering to obtain the N1,N2,N4,N5-tetra(2-sulfydrylethyl)1,2,4,5-pyromellitic formamide. The sulfide heavy metal chelating agent provided by the invention is used for treating industrial wastewater containing heavy metal ions and can effectively avoid the generation of hydrogen sulfide; the sulfide heavy metal chelating agent can be rapidly reacted with various heavy metal ions in the wastewater at a room temperature to generate water-dissoluble sulfide sediment; the sediment is large in grain size and compact in flocs, so that the deposition time is shortened, heavy metal can be recycled from residues, and secondary pollution is not easy to happen. The sulfide heavy metal chelating agent N1,N2,N4,N5-tetra(2-sulfydrylethyl)1,2,4,5-pyromellitic formamide and the preparation method thereof, provided by the invention, have the advantages of simple preparation process, convenience for use and good treatment effect.