Abstract: Results from experimental and numerical analysis on SRC columns generally do not agree well at present. The main reason may be the lack of understanding on the confinement mechanism, as well as the application of corresponding stress-strain model for steel confined concrete. In this paper, the confinement mechanism of concrete by cross-shaped steel with flanges is studied in depth based on previous experimental results on steel confined concrete. Firstly, a simplified distribution of lateral stress imposed by steel confinement to concrete is proposed, based on which steel confined concrete was divided into three regions, including strong steel confined concrete, weak steel confined concrete and steel non-confined concrete. Confinement factors reflecting the confining level of steel to concrete for each region of the confined concrete were determined by calculating the effective lateral confining pressure. Based on Mander's model for stress-strain relationship of concrete considering the confining effect from spiral stirrup reinforcement, a unified stress-strain model for steel confined concrete is developed by modifying the key parameters of Mander's model. It is proved by comparing the results from experiment and numerical simulation utilizing the proposed stress-strain model that the confinement mechanism and the constitute model for steel confined concrete established in this paper are reasonable and effective.