In order to investigate the strengthening effects of different types of FRP sheets on the mechanical properties and failure modes of square concrete columns, 1/4 arc was adopted to replace the traditional second-degree parabola to distinguish the effective confinement area from weak area. Then the shape coefficients were improved and unified into one for purpose of engineering application. The performance of the five strength models after improvement was evaluated based on the analysis of 138 experimental columns strengthened by different types of FRP sheets. Satisfactory agreements between the improved models and the experiments were found. In order to extend the application range of the improved models, 8 BFRP jacketed concrete columns were further tested. Result shows the improved models is capable of predicting the bearing capacity of BFRP jacketed concrete column in predicting the load capacities of such columns was confirmed.