Abstract [Objective] The paper was to study in vitro pharmacodynamics character- istics of florfenicol dual suspension emulsion （DSEF）. [Method] The florfenicol injec- tion （FI） was used as the control group, the minimal inhibitory concentration （MIC）, minimal bactericide concentration （MBC） and mutant selection window （MSW） of florfenicol dual suspension emulsion on 5 kinds of bacteria were determined. The post-antibiotic effect （PAE） and post-antibiotic sub-MIC effect （PASME） of Salmonella typhimurium were also measured. [Result] Compared with the ordinary injection, the MIC and MBC of florfenicol dual suspension emulsion on 5 kinds of bacteria showed no obvious changes. However, florfenicol dual suspension emulsion obvious- ly narrowed MSW of 5 kinds of bacteria （P〈0.01）, which also significantly extended PAE and PASME of S. typhimurium （P〈0.01）. [Conclusion] The florfenicol dual sus- pension emulsion in vitro can reduce the probability of bacterial resistance, signifi- cantly prolong after effect time of antibiotics on bacteria, thereby effectively improving the antibacterial effect.