OBJECTIVE To study the changes in air bacteria content under gradual circuit model and ordinary circuit model in operating room.METHODS Altogether 80 cases with thyroid gland surgery and gastrointestinal surgery were selected,and divided them randomly into two groups: the gradual circuit model and the ordinary circuit model,each group had 40 cases.The period of early morning to the end of operation was divided into 10 time spots to carry on the air bacilliculture.RESULTS Under the ordinary circuit model,air colony showed straight up with time during the two types of surgical operations,and there was no significant difference between the two types of surgery.Under the gradual circuit model,air colony began to increase with time,followed by steady,or even decline,no differences between the two types of surgery. Roving between two models,significant statistical difference emerged in thyroid surgery from the 30-minutes of operation(P