Terahertz (THz) wave has broad application prospects because of its many unique properties. However, due to the relative lag in the development of related materials and devices, there are still many limitations in the practical application of terahertz technology. Metamaterials and metasurfaces can effectively manipulate the phase, amplitude, and polarization of terahertz waves, providing many new possibilities for the development of terahertz technology. One of its important functions is to reflect incident waves in non-specular directions through phase discontinuities, commonly known as generalized Snell's law. However, most of the previously reported anomalous reflection devices are relatively inefficient and have limitations in practical applications. To solve this problem, we propose a terahertz metasurface anomalous reflector that reflects normal incident light to a 40° direction without changing its polarization. We theoretically expound the idea of improving efficiency and demonstrate its effectiveness through numerical simulation. We construct a metasurface using all-dielectric materials to eliminate material losses and exploiting the coupling of different Bloch waves to provide a non-local response, the operating efficiency of the device can be increased to more than 99%. In addition, our design concept can be generalized to polarization-independent devices and could be useful for other similar devices. This work has the potential to be applied to practical terahertz devices such as terahertz lasers and terahertz cavity resonators.