The utility model relates to a purifying device used in a cold rolling mill for purifying phosphate fog generated from a hot galvanizing machine set, which mainly comprises a horizontal purifier (8) and a ventilating device, wherein, the ventilating device essentially consists of a centrifugal ventilator (15), am electric motor (13), an electric control valve (16) and a ventilating duct,wherein, an inlet and an outlet of the centrifugal ventilator are respectively connected with a blast pipe (11) and an exhaust duct (18) through a flexible connector (17); the electric control valve is arranged between the blast pipe and the inlet of the centrifugal ventilator; the horizontal purifier is arranged between an air inlet pipe (6) and the blast pipe (11). The purifying device can be used in the cold rolling mill for purifying phosphate fog generated from a hot galvanizing machine set with small spangle technique, has high purification effect without causing secondary pollution, is convenient to adjust the wind volume and the wind pressure, can reduce the resonance vibration caused by the vibration which is generated in the operation of the purifying device and is transmitted to pipe fittings and the steel structure connected with the purifying device, and has the advantages of compact structure, convenient operation, maintenance, repair, etc.