Abstract: Based on a shear experiment of 12 prestressed I-steel ultrahigh reinforced concrete beams and 2 prestressed I-steel ordinary reinforced concrete simply supported beams, the main factors affecting the shear performance of a prestressed I-steel ultrahigh reinforced concrete beam were revealed and the influences of the shear span-depth ratio, the space of stirrups, the thickness of web, the compressive strength of concrete and the degree of prestress on the failure mode, the load-deflection curve, the first shear crack load and the shear capacity of test beams were investigated. The experimental results show that prestressed I-steel ultrahigh reinforced concrete beams have better shear capacity and shear ductility, as well as higher stiffness than those of prestressed I-steel ordinary reinforced concrete beams. In addition to the experimental results, a new method for predicting the shear capacity of prestressed I-steel ultrahigh reinforced concrete beams is proposed. The proposed method gives satisfactory predictions as compared to the experimental results. The research achievements are expected to provide a theoretical support for the design calculation and engineering application of prestressed I-steel ultrahigh reinforced concrete beams.