Objective To study bacterial conditions in amniotic cavity of the third trimester and the delivery. Methods Patients underwent cesarean section due to various reasons were randomly enrolled in the study. Ten ml aqua amnii taken from using aspesis were cultured and the bacteria were identified and tested for drug sensitivity. All patients were not treated with antibiotics before and during operation,conventional antibiotics treatnent was used after operation. The patients were divided into 3 groups based on their status: 34 cases of premature rupture of membrane ( PROM ), thirty-four cases of labor without PROM, and 27 cases of pregnancy without PROM. The positive rate, species , distribution and drug sensitivity of bacteria in the 3 groups were analyzed. Results The positive rate was 61.8% (21/34) in PROM ,52. 9% ( 18/34 ) in labor without PROM,11.1% (3/27)in pregnancy without PROM. The positive rates were significantly different among the 3 groups (x2 = 17.29 ,P =0.000). However, there was no significant difference between the labor without PROM group and the pregnancy without PROM group ( x2 = 0.541 , P = 0.462 ). Staphylococcus epidermidis was the most common isolated bacteria, following by staphylococcus aureas, streptococcus, colon bacillus, and pseudomonas. There were no significant differences of bacterial species between labor without PROM and pregnancy without PROM( x2 = 11.9,P =0.535 ). The relative higher positive rate in the labor without PROM and PROM indicated that they were important inducement of bacteria infection. There were no significant difference on positive rate and bacteria species distribution between the PROM and labor without PROM group,which suggested that up-bound along vagina to amniotic cavity was the most common route of infection. Sensitive antibiotics should be given to the patients of PROM and labor without PROM targeted at staphylococcus,streptococcus, colon bacillus and monad. Antibiotics such as Cephems, Penicillins and Clindamycin were sensitive to various bacteria and safe to both mother and baby, thus were recommended. Quinupristin, Vancomycin,Furantoin, Fusidic ,Teicoplanin, Amikacin and Meropenem were also sensitive to various bacteria, but due to their side effects and the principle of ladder antibiotics using, they were recommended as second line antibiotics. Conclutions Up-bound along vagina to amniotic cavity is the most common route of infection. For rupture of membrane and labor without PROM patients, antibiotics should be given, and strict aseptic technique,washing cavity and incision, using antibiotics after operation are necessary to prevent infection.