Due to porous materials have unique pore structure， it can be used in the field of acoustic noise reduction and flow control. Firstly， the large eddy simulation （LES） method is used to simulate the flow around a circular cylinder with or without porous medium at subcritical Reynolds number. Secondly， the lift and drag coefficients under two different working conditions are compared， and the drag reduction control effect of porous medium is analyzed. Finally， the drag reduction control mechanism of porous medium is revealed by combining aerodynamic force and flow field structure changes. The results show that at the Reynolds number of 5.6×10⁴， the maximum drag reduction rate is reached to 8.53% when the porous medium is laid at azimuth angle of 270° at the leeward side of the cylinder surface. On the one hand， due to the permeability of porous medium， it can imporve the slip velocity at the interface between porous medium and fluid， stabilize the separated shear layer on the cylinder surface， and reduce the vortex frequency. On the other hand， the fluid can pass through porous medium， then produce the effect similar to micro-jet， which enhance the pressure on the cylinder surface in the separation zone， and significantly reduce the pressure difference between the upstream and downstream of the cylinder and the total drag on the cylinder surface.