High-temperature electronic equipment dissipates heat by receiving cooled air from environmental control devices for effective heat dissipation. Due to space constraints and equipment operating environmental conditions, it is common to provide cooling air at a distance using air ducts. In this case, uniform and stable supply of cooling air is most important. But, the ducts are accompanied by flow losses and pressure variations due to changes in flow cross-sectional area, internal surface conditions, and flow velocity, and in particular, there is a difference in air flow characteristics depending on the cross-sectional shape of the duct. In this paper, the air flow performance of straight duct and flexible duct is compared by CFD(Computational Fluid Dynamics) analysis. As a result, it was confirmed that the air flow nonuniform and instability occurred due to the frictional resistance and the pressure difference of the flexible duct’s wrinkled portion.