Abstract: In the design of a concrete frame structure, the stiffness of concrete frame beams should be amplified because of the spatial composite effect of floor slabs and concrete beams. In view of the concrete frame beam stiffness amplification factor, a beam-shell mixed elaborate model is established to simulate the actual working state of concrete frame beams and slabs, and the main parameters affecting the stiffness amplification factor are analyzed upon the beam-shell finite element model proposed. An extensive parametric analysis on the concrete frame beams under different load cases are conducted. Then, a simplified calculation formula for the stiffness amplification coefficient of the concrete frame beam is proposed, and the accuracy of the formula is verified by simulation-based verification of a concrete frame system with different parameters. It can be found that finite element models which do not consider the space composite effects of floor slabs have significant errors compared to refined finite element models, while finite element models which using the stiffness amplification factors proposed by this article fits well with the beam-shell mixed finite element model in terms of parameters such as periods, lateral displacements, maximum storey drifts, structural internal forces, and vertical deflections.