Abstract: Fiber reinforced polymer (FRP) bar, as a non-corrosive alternative material to steel bar, it has become a viable solution for corrosion problems of steel. FRP bars have been widely used in prestressed structures, offshore platforms, coastal wharfs and components exposed to long-term corrosion chemical environments. At present, the design method of pure torsional capacity of FRP reinforced concrete members is seldom proposed except for the CSA S806-12. It is primarily presented in a modified form of the existing formula for calculating the pure torsional capacity of reinforced concrete members, considering the difference of material mechanical parameters between FRP bars and steel bars. In this paper, a pure torsional failure behavior of FRP reinforced concrete columns with a maximum cross-section width of 1000 mm was studied and, the size effect law of nominal torsional strength was revealed by using inspected three-dimensional meso-numerical simulation methods. Based on the simulation data, the existing calculation formulas of the pure torsional capacity of FRP reinforced concrete members were compared. In addition, upon the GB 50010−2010 on the calculation method of pure torsional capacity of reinforced concrete components, a calculation method of pure torsional capacity of FRP reinforced concrete members considering size effect was proposed. By comparing the existing test data, the correctness and rationality of the proposed formula were verified.