Abstract: In view of the reservoir geologic features and special geographic environment of Bohai SZ36-1 oilfield,and through interfacial tension test,alkali consumption test and emulsification test,the combination flooding formula in Bohai SZ26-1 has been worked out.After comprehen sive consideration of the factors such as scale,the opti- mized formula is:Na_2CO_3 4000 mg/L+petroleum sul- fonate 500 mg/L+3630S 1000 mg/L,which can lower the oil-water interfacial tension to 10-3 mN/m and has sumption,good resistance to Ca~(2+) and Mg~(2+),and easy demulsification of emulsion liquid.Physical model test in- dicates the formula can enhance the recovery of 19.15% on water flooding and have great application potential for offshore oilfield.