The present application belongs to the technical field of protein extraction and particularly relates to a system for extracting whey protein powder from soybean protein waste water. The system successively comprises an air flotation machine, a residue storage tank, a stack screw, a stirring and diluting tank, a plate-and-frame filter pressing machine, sub-belts, a gathered belt, a crusher, a wetmaterial cabin, a hollow blade dryer, a vibrating sieve, a cyclone dust remover, a finished product material cabin and an automatic packaging machine in pipeline connections, the air flotation machineis connected with an inclined plate sedimentation tank via a pipeline, the inclined plate sedimentation tank is connected with an anaerobic system via a pipeline, and the inclined plate sedimentationtank communicates with the residue storage tank via a pipeline. Beneficial effects are as follows: by extracting residual small-molecular proteins in the protein waste water for resource utilizationand at the same time reducing impacts of suspended solids (the small-molecular proteins) on a waste water treatment system, the product whey protein powder is formed. The system solves the impacts onthe waste water treatment system and also solves environmental problems that wet protein residues are easy to decay and deteriorate.