Abstract: Two kinds of fungicides named Dodecyl dimethyl benzyl ammonium chloride(1227) and isothiazolinone （Kathon 886）were experimentally tested in the lab individually or mixed use in order to investigate their sterilization rate and compatibility with polymer. Test indicates that the mixed usage of two agents with the mass ratio of 1:3 (1227: Kathon 886) achieves better effect than two kinds of fungicides used individually and exhibits a high compatibility with polymer for enhanced oil recovery (EOR), indicating the synergetic effect exists. Under the conditions of no oxygen atmosphere, 53℃ and 90 day aging, the polymer viscosity retention rate is 64.7%. It is concluded that the composite fungicide can be used as a new type of high-effect fungicide in polymer flooding for tertiary oil recovery process.