Abstract: Large amount of PH<SUB>3</SUB> tail gas will be produced in the production of sodium hypophosphite (NaH<SUB>2</SUB>PO<SUB>2</SUB>).Generally,the tail gas will be burnt to prepare H<SUB>3</SUB>PO<SUB>4</SUB>.The main equipments include combustion tower,absorption tower and dust collector etc..The capacity and separating efficiency of the dust collector will directly affect the quality of products and the content of H<SUB>3</SUB>PO<SUB>4</SUB> in the exhaust gases.The limitations of the dust collector in the production，such as small treating capacity and low efficiency etc.,were analyzed in this paper.Furthermore,the venturi-duct,nozzle and cyclone separator,which have influence on the treating capacity and dust collecting efficiency were re-designed and optimized.The newly designed venturi-duct dust collector was characterized by large treating capacity,high efficiency and low resistance.Practice has proved this design plan to be feasible.<BR>