In this work, energy-variational principle was used to study the local buckling performance of rectangular section CFT columns with stiffeners. The buckling coefficient of the rectangular plate with stiffeners was obtained via using the Rayleigh-Ritz energy approach. Furthermore, the minimum stiffness requirement was deduced. Then, the influencing factors on the minimum stiffness were analyzed. It was manifested that the minimum stiffness was affected by As/bt, the width to thickness ratio of steel plate, yield strength of steel and flexural rigidity of steel plate in steel tube. The minimum stiffness increased with the increase of the width to thickness ratio of steel plate. The minimum stiffness decreased with the increase of the number of longitudinal stiffener. Finally, parametric analysis was conducted using the commercial finite element software ABAQUS, and the accuracy of the finite element model was verified by a large number of tests. It was shown that the correctness of analytical solution proposed here agreed well with the numerical simulations. Numerical simulations disclose that when the setting of longitudinal stiffeners meets the minimum stiffness requirement, the rectangular section CFT columns with large ratio of width to thickness shall be full-section efficient and can be designed according to the relevant codes in China.