Abstract: In order to study the size effect of shear performance of UHPC beams without Stirrups, designed were six UHPC test beams without Stirrups, with a span ratio of 2 and effective section height of 150 mm~490 mm. The influence of steel fiber content on the shear performance of the beam was considered. By analyzing the test phenomena, load-deflection curves, and compressive strain of concrete curved arches under the shear action of test beams, ductility and deflection-span ratio of beams, discussed was the size effect mechanism of shear performance of UHPC beam without Stirrups. The results show that there is a size effect on the shear resistance of UHPC beams without Stirrups, and that the larger the size of the beam, the smaller the nominal ultimate shear stress. With the increase of the test beam size, the deformation capacity of the beam gradually decreases, the stiffness and brittleness increase, and the bridge connection of steel fiber weakens. In this study, considering the size effect of concrete arches under the shear action of beams, the shear bearing capacity model of UHPC beam without Stirrups is derived, and the calculated values of the model are in a good agreement with the test values with little variability.