To study the antibacterial effect of eight kinds of Chinese drugs in vitro，screen the best compound ratio for external use to treat acne and prepare compound microemulsion gel for in vivo pharmacodynamic study of acne model in mice.

Propionibacterium acnes and Staphylococcus aureus were selected as target bacteria，and the diameter of inhibition zone and minimum inhibitory concentration（MIC）of eight Chinese drugs were determined by filter paper method. Orthogonal test was used to optimize the compound ratio. The physical and chemical properties of microemulsion and microemulsion gel were comprehensively evaluated by preparing microemulsion with pseudo ternary phase diagram as evaluation index. A mouse acne model was established by injecting Propionibacterium acnes into the back，and the blank group，model group，positive drug group，microemulsion gel group and compound microemulsion gel group were set up. Histopathological changes were observed by HE and Masson staining，and the levels of inflammatory factors［interleukin-1β（IL-1β），interleukin-10（IL-10）and tumor necrosis factor-（TNF-α）］in serum were detected by enzyme-linked immunosorbent assay（ELISA）.

The results showed that all the eight Chinese drugs had different antibacterial effects，among which Huanglian（Coptidis Rhizoma）had the best antibacterial effect on Propionibacterium acnes and Gancao（Glycyrrhizae Radix et Rhizoma）had the best antibacterial effect on Staphylococcus aureus，with MIC of 31.25 mg mL^-1. The orthogonal test results showed that the sterilization rate of Dahuang（Rhei Radix et Rhizoma）（250 mg mL^-1），Huanglian（Coptidis Rhizoma）（250 mg mL^-1），Huangqin（Scutellariae Radix）（125 mg mL^-1）and Gancao（Glycyrrhizae Radix et Rhizoma）（62.5 mg mL^-1）was the best when the ratio was 4∶4∶2∶1. According to the pseudo-ternary phase diagram，the final microemulsion formula was Tween-80（3 g），PEG 400（6 g），isopropyl myristate（1 g）and distilled water（12 g），and 1% carbomer 940 was added according to the mass ratio，and the microemulsion gel was obtained after full swelling，and the compound microemulsion gel was obtained by replacing the water phase with the compound extract of the Chinese medicine compound. The pharmacodynamic experiment showed that compared with those of the blank group，the skin tissue of the model group showed obvious pathological changes，and the contents of IL-1β，IL-10 and TNF-αin serum increased significantly（P<0.01）. Compared with those in the model group，the pathological changes in the drug group were relieved to varying degrees，and the contents of serum inflammatory factors were decreased，especially those in the compound microemulsion gel group（P<0.01）.

The compound of Dahuang（Rhei Radix et Rhizoma），Huanglian（Coptidis Rhizoma），Huangqin（Scutellariae Radix）and Gancao（Glycyrrhizae Radix et Rhizoma）has obvious bacteriostatic effect. The preparation of the compound microemulsion gel has a good therapeutic effect on acne model in mice，and can effectively alleviate acne inflammation caused by Propionibacterium acnes.