A method of synthesizing a high purity product of α,α,α′,α′-tetrachloro-p-xylene is disclosed. The method includes carrying out a first stage reaction of terephthaldicarboxaldehyde with a mixture of SOCl2 and dimethylformamide (DMF) to obtain a product mixture containing α,α,α′,α′-tetrachloro-p-xylene as a major product and 4-dichloromethyl benzaldehyde as a side product; adding SOCl2 and DMF to the product mixture of the first stage reaction to undergo a second stage reaction; and to a cool water adding the resulting product mixture from the second stage reaction to obtain a solid product of α,α,α′,α′-tetrachloro-p-xylene with a purity of 90-99 mol %.