The invention provides a method of preparing 1,2,4,5-tetra amino benzene and hydrochloride thereof. 4,6-dinitro m-dichlorobenzene is used as a raw material, and the 1,2,4,5-tetra amino benzene is prepared through aminolysis and catalysis hydrogenation reduction and the hydrochloride of the 1,2,4,5-tetra amino benzene is prepared by adding hydrochloric acid. The method has advantages of easily-available raw materials for the reaction, few side reactions and controllable amount of byproducts. The hydrochloride of the 1,2,4,5-tetra amino benzene has a purity up to a polymer grade requirement, and a total yield of more than 75 %. A thermal decomposition temperature of the 1,2,4,5-tetra amino benzene is 200-282 DEG C detected by a thermal gravimetric method. The 1,2,4,5-tetra amino benzene is good in thermal stability. As a new synthetic material monomer, the 1,2,4,5-tetra amino benzene with a purity of more than 99 % is used to polymerize with 2,5-dihydroxy terephthalic acid to prepare poly-1,4-(2.5-dihydroxy) phenylene benzo diimidazole resin with an intrinsic viscosity Eta of more than 12 dL*g<-1> and a good spinnability.