A efficient 3D beam element based on the distributed nonlinearity theory is proposed for nonlinear analysis of reinforcement concrete structures. The sections consist of reinforcing steel and concrete in this formulation and the section stiffness matrices are calculated through the integration of stress-strain relations of concrete and the accumulation of reinforcing steel effect. The force-based formulation is adopted in the evaluation of the element stiffness matrix and the element state determination. The improved Kent-Park model is adopt for the stress-strain relation of concrete, and uniaxial stress–strain relationships proposed by Mander is introduced for reinforcing steel. Finally, the ultimate load of a cantilever reinforced concrete beam subjected to a lateral load was analyzed with the proposed formulation to illustrate its accuracy and computational efficiency.