The invention relates to a preparation method of m-dichlorobenzene. The preparation method comprises adding a metal porphyrin complex into benzene, introducing chlorine gas into the mixture, carrying out a chlorination reaction process at 70 to 120 DEG C under reaction pressure of 1-4 atms for 2-7h, adding a solid super acid into the chlorination reaction product mixture, and carrying out a reaction process at a temperature of 120-140 DEG C for 1-4h to obtain m-dichlorobenzene, wherein a mole ratio of benzene, chlorine to metal porphyrin complex is 1: 2.3: 0.0001-0.1. The preparation method of m-dichlorobenzene has the advantages of high conversion rate, good selectivity and high yield.