The invention discloses a synthesizing method and application of 1,2,4,5-tetraamine benzene. The synthesizing method comprises the following steps: preparing a chlorobenzene byproduct which is 1,2,3-trichlorobenzene as a raw material; nitrifying to obtain 4,6-binitro-1,2,3-trichlorobenzene; further performing ammonolysis in an organic solvent A to obtain 4,6-binitro-2-chlorine-1,3-phenylenediamine; dissolving an ammonolysis product into an organic solvent B; performing catalytic hydrogenolysis to obtain 1,2,4,5-tetraamine benzene. Compared with the prior art, the method has the advantages thatthe chlorobenzene byproduct which is 1,2,3-trichlorobenzene is utilized, and moreover, nitroreduction and halogen hydrogenolysis are integrated during the hydrogenolysis process, thereby facilitatingindustrial production, and providing raw material support to development of downstream products. The application is that 1,2,4,5-tetraamine benzene is used as the raw material and polymerized with 2,5-dihydroxy terephthalic acid to obtain PDBI resin which is an engineering fiber material being high in spinnability and high in modulus.