The invention discloses a stainless steel slag treatment device and a treatment method thereof. The stainless steel slag treatment device comprises a slag pot arranged on a slag pot supporting seat, afixed frame arranged on a foundation, a dust removal cover with a dust removal opening, a swing arm, a hydraulic cylinder, a water supply pipe, a water supply control valve, an atomizing nozzle, a moving exhaust pipe, a fixed exhaust pipe and an air draft control valve, wherein one end of the swing arm is hinged to the fixed frame and the other end of the swing arm is fixedly connected with the outer side of the dust removal cover, the hydraulic cylinder is used for driving the swing arm to swing around a hinged point to realize that the dust removal cover covers and opens the slag pot, the water supply pipe is arranged on the fixed frame and the swing arm, the water supply control valve is arranged on the water supply pipe, the atomizing nozzle is arranged at the tail end of the water supply pipe and located on the inner side of the dust removal cover, the moving exhaust pipe is fixedly connected with the outer side of a dust removal opening, the fixed exhaust pipe butts against themoving exhaust pipe through a water sealing connector, and the air draft control valve is arranged on the fixed exhaust pipe. The stainless steel slag treatment device has a cooling effect, realizes synchronous collection of steam containing dust and poisonous gas, avoids leakage, and has high automation degree and simple structure.