Abstract: The influence of the structural parameters of a multi-sectional long thin tube on the pressure drop characteristics of a deflation system is studied by numerical simulations, and the relationship between the structural parameters and the pressure drop characteristics is obtained. The results indicate that the flow velocity of the gas under laminar flow conditions is greatly increased by decreasing the length or increasing the inner diameter of the tube, but the pressure drop under chocked flow conditions is hardly affected by the change of structural parameters. The roughness of the inner tube has a great influence on the pressure drop under chocked flow conditions, but has a smaller influence on the pressure drop under laminar flow conditions. It is also found that the outlet pressure has nearly no influence on the deflation velocity during the whole flowing process, which means that the deflation velocity will not be increased by increasing the outlet pressure. These results provide some guidance for optimizing the design of small- diameter tubes in the deflation system.