Abstract: Ultra high performance concrete (UHPC) is a remarkable material exhibiting higher strength, toughness, durability and anti-impact property when compared with conventional concrete. In the study of deformation and stiffness of UHPC beams, the immediate stiffness calculation theory has not yet formed a unified method. In this study, the UHPC immediate stiffness calculation method was derived by using the effective inertia moment method and the stiffness analysis method respectively combined with the material properties of UHPC. Through experimental investigations of 12 UHPC test beams, it is found that the immediate stiffness was better calculated by the two immediate stiffness calculation methods and the accuracy satisfied engineering requirements. Compared with the stiffness analysis method, the values calculated from the effective inertia moment method were closer to experimental values.