Abstract: This study proposed a prefabricated ultra-high ductility concrete (UHDC) beam permanent formwork that is easy to produce and transport, and investigated the shear performance of the beams built by UHDC formwork. Nine RC beam specimens were tested by four-point bending test, the effects of formwork form, of formwork material and, of shear span ratio were investigated on the failure mode, on the shear bearing capacity and, on the deformation capacity of beams. The result showed that: Under the same parameter configuration, the stiffness, shear cracking load and ultimate shear bearing capacity of the beams with UHDC formwork were significantly higher than those of ordinary RC beams, but the ductility reduced due to the occurrence of interface shear failure; The shear behavior of the beam with assembled UHDC formwork was very close to that of the beam with integral U-shaped formwork; Embedding carbon grids into UHDC formwork could further improve the ultimate shear bearing capacity of the beam, but the enhancement was relatively small; As the shear span ratio increases, the improvement of the shear bearing capacity caused by carbon mesh decreases. Finally, based on the truss-arch model, considering the effective shear contribution of UHDC formwork under different failure modes, a calculation method for the shear bearing capacity of the beam with UHDC formwork was proposed.