Abstract: In seqtember 1995, we tested the biological clean degree of No. 7 operation room in our hospital. By using ANDERSEN biological ions, the air of No. 7 operation room were 24 cfu/m³ after it had been used 10 months. This datum was amounting to the standard of biological clean grade Ⅱ in our country （as the Grades Ten Thousand Purification Standard） and going beyond the Biological Purification Grades Ten Thousand of NASA. The distribution of biological ionic concentration in the air of the room showed as “V” shape. The rate of biological ion of the Grade Sixth （＜0.65 μm） was greater and accounted for 26.0%. Opening the door of operation room, and incoming and out going personnels from the room were factors that influenced the clean degree in the room air. In order to reduce the chance of surgical infection the door of operation room ought to be closed and personnels in operation room showed be controlled as far as possible during an operation is going on.