A good modeling of the stress–strain behavior of FRP-confined concrete prism is necessary for the design of rectangular columns retrofitted with FRP composites. Existing stress–strain models for FRP-confined concrete prisms are mostly presented based on the concept of steel-confined concrete columns. Based on the results of more than one hundred specimens, the mechanical behavior of FRP-confined concrete prisms are studied in this paper. It is found that the stress–strain relationship of FRP-confined prism has either a strain-hardening or a strain-softening response, which mainly depends on the confinement strength of FRP, corner radius of cross-section, etc. Equations to predict the transitional stress and strain of FRP-confined concrete prisms are presented. By reducing the corresponding ultimate strength and strain of equivalent concrete cylinders confined with equivalent FRP, the ultimate strength and strain of FRP-confined concrete prisms can be predicted rationally. Three design-oriented models, which can be applied to various conditions, are suggested. The feature of those models is simple, and they agree well with extensive experimental results.