Abstract: By wind tunnel tests, Reynolds number effect on drag force coefficient, lift force coefficient and wind pressure coefficient of cylinder were measured, the mechanism of the aerodynamic force variation from the point of view of the flow field distribution was analyzed, and the correlation of the flow field in the cylinder axis direction under the Reynolds number effect was studied. Results show that in the subcritical Reynolds number regime, the time averaged flow field around the cylinder model is symmetric, the Reynolds number has little influence on the averaged drag force coefficient and flow field, and the averaged lift force is around zero. In the critical Reynolds number regime, with the appearance of large amplitude negative pressure in certain areas, flow field becomes asymmetric, and the averaged lift force as well as fluctuation lift force appears. In the supercritical Reynolds number regime, with the appearance of large amplitude negative pressure on the two sides, flow field becomes to symmetric again, and the averaged lift force disappears. Reynolds number has obvious effect on the flow field correlation along the cylinder axis. In the subcritical Reynolds number regime, the scale of the Karman vortex in the cylinder axis direction is relatively large, while the scale becomes small with the increase of Reynolds number.