The invention relates to a machining device, in particular to a distributive dust purifying device for a grinding machine, and solves the problem of weaker dust removing effect in a traditional tablegrinding machine. The device comprises a grinding machine, a grinding wheel, a negative-pressure chamber, a window, an isolation chamber, a filter, an upper support plate, a lower support plate, a middle support frame, an air filter paper, a conical body, a reverse blowing device, a pulse electromagnetic valve, a reverse blowing pipe, a fan, a hose, a spraying dust remover, a tank, an air exhaustport, a settling port, a screen plate, a nozzle and a water pipe. The device cannot pollute the workshop environment, is excellent in dust removing effect, and meanwhile, meets the air exhaust requirements.