Abstract: In the transonic wind tunnel, the flow of wet air can turn into non-isentropic flow due to water vapor condensation in the test section, followed by the formation of condensation wave, seriously destroying the uniformity of the flow field and the accuracy of the test data. Therefore, the air should be dried ahead of test to ensure its moisture content less than 1.5 g/kg. The circulation drying system is an economical and efficient air-drying way in the large continuous transonic wind tunnel. In this paper, a rotary and cooling dehumidification drying system is designed for the wind tunnel, and an air-drying calculation model based on the assumption of uniform mixing is proposed and validated by experiment. According to the proposed model, the optimized parameters of the air-drying system are obtained. The results show that the model can effectively estimate the change of the average moisture content in the tunnel, and the deviation from the test is within 8.3% when the number of cycles is more than 2; the maximum cooling load of the front and rear heat exchanger can be reduced by about 41.9% and 27.8% respectively in this system by making full use of the dehumidification capacity of the first four cycles and the selected rotary dehumidifier.