The invention relates to a converter steel slag treatment device which comprises a crown block, a slag ladle, a chute, a forklift, a steel slag pool, a bottom filtering pool, a water pump house, a water storage tank, a cooling tower, a bridge-type grab crane, a chimney, a hydraulic roller couple, nozzles, a granulating room and a condensate water tank, wherein a lifting hook of the crown block is connected with the slag ladle, the outlet of the slag ladle is connected with the inlet of the chute, and the outlet of the chute is connected with the upper part of the hydraulic roller couple; nozzles a are symmetrically arranged on the two sides of the upper part and the two sides of the lower part of the hydraulic roller couple, and the hydraulic roller couple and the nozzles a are all arranged in the granulating room; the steel slag pool is arranged at the lower part of the granulating room, and the forklift is arranged on the outer side of the lower part of the granulating room. The invention further discloses a converter steel slag treatment method. The flow of the method is as follows: steel slag dumping, steel slag crushing, steel slag granulating, slag washing water filtering and vapor condensation recovery. The converter steel slag treatment device has the advantages of high slag treatment efficiency, compact occupied area, energy conservation, environment protection and no pollution, adapts the fast-paced production mode of a converter, is good for magnetic separation extracting of grain steel and comprehensive application of grain slag, and has remarkable economical benefit.