The invention relates to a treatment method of tar-containing wastewater for tail gas purification of a calcium carbide furnace, wherein a buffer pool, a lifting pump, a tar settling tank, a demulsification tank, a flocculation tank, a floatation tank and a homogenous adjusting pool are sequentially connected. The method provided by the invention respectively separates heavy oil and light oil in tar by adopting the process technologies of thermochemical sedimentation and dissolved air flotation to realize automatic operation of the device. Meanwhile, the content of tar in the tar-containing wastewater, concentration of ammonia and concentration of volatile phenol in tail gas purification of the calcium carbide furnace are reduced, so that the deficiencies in the prior art are overcome, and the content of tar in the tar-containing wastewater is reduced to below 1mg/l. Compared with the prior art, the treatment effect of the tar-containing wastewater is effectively improved, and the method has the advantages of less pollution, feasible process technology and safety and stability and can realize the purpose of reducing the content of tar, concentration of ammonia and concentration of volatile phenol in the tar-containing wastewater, and realize energy conservation and emission reduction and protect the environment. The method provided by the invention can be widely applied to the tar-containing wastewater treatment technology.