The invention discloses a sulfydryl-modified molybdenum sulfide quantum dot, a preparation method of the sulfydryl-modified molybdenum sulfide quantum dot and a detection method of 2,4,6-trinitrotoluene, wherein the method comprises the following steps of 1, firstly mixing hydroxylamine hydrochloride, molybdenum disulfide and solvents; then, performing heat treatment; next, performing centrifugal purification so as to prepare the sulfydryl-modified molybdenum sulfide quantum dot; (2) mixing the sulfydryl-modified molybdenum sulfide quantum dot, sulfydryl-containing compounds and the solvents; then, performing contact reaction so as to prepare the sulfydryl-modified molybdenum sulfide quantum dot. The sulfydryl-modified molybdenum sulfide quantum dot prepared by the method has the advantages of high quantum yield, strong anti-jamming capability and good stability. In addition, the sulfydryl-modified molybdenum sulfide quantum dot prepared by the method has the good selectivity on the detection of the 2,4,6-trinitrotoluene solution concentration.