Abstract: Three standard and two isolated strains of E.coli were used for drug sensitivity test on Chloramphenicol, Ciprofloxacin Lactate, Rifampicin, sulfamonomethoxine, Florfenicol, Ceftiofur Sodium as well as the antimicrobial synergists sulbactam sodium and TMP. The bacteriostasis results of the antibiotics against E.coli In vitro were compared when they were used separately or combined with the synergist. The result showed that:(1) E.coli has no resistance against Ceftiofur, and others showed various degrees of resistance; (2) the resistant result was apparent when Ceftiofur was used together with sulbactam or TMP at a ratio of 3:1, so the effect of Ceftiofur could be enhanced by sulbactam or TMP, and sulbactam worked better than TMP.