Abstract: The U. S. S. R. professor L. M. Marlanbarh studied cupola of three line tuyere hole. He pointed out that the air volume ratio of tuyere can be replaced by the tuyere area ratio, and cupola can be designed according to this viewpoint. Nowadays' two line tuyere hole cupolas are being designed in this way at home and abroad. This point has been in the field of technology for mang years,it proposes that the flow rate of tuyere holes are equal to each other' but there is no experiment evidence to prove this point.The article suggests a new method of measurement' using a probe to measure the blowing rate of tuyere hole. The result has proved that the air volume ratio of tuyere cannot be replaced by the tuyere area ratio,the flow rate of the tuyere holes are not equal to each other, the blowing rate is related to the .structure of air belt and the position of air pipe This article suggests a newtheory principle of the cupola design.