Six rectangle steel tube confined concrete columns were investigated experimentally under axial compression. The experimental results show that:The rectangle steel tube can effectively confine internal concrete and obviously improve the peak stress. In addition, the descending branch of confined concrete stress-strain curve is gentler and the ultimate deformation ability of concrete is improved effectively. On the basis of experiments, a method to calculate the effective transverse confined stress provided by the rectangle steel tube was proposed through analyzing the strain of steel tubes and the stress state of core zone concrete. Furthermore, a model to determinate the stress-strain relationship of rectangle steel tube confined concrete under axial compression was put forward reference to the Mander's model. Computation results of the stress-strain curve of rectangle steel tube confined concrete were in good agreement with the experimental results.