In recent years, with the development of heterodyne array receivers of radio frequency (RF) telescope, beam splitters based on phase grating technology have gained important applications in the sub-millimeter wavelength range. It is capable of transmitting a single local oscillator signal to the superconducting SIS/HEB mixer receiver array by splitting beam synchronization. Due to the characteristic size of the terahertz phase grating at sub-micron level, its machining precision directly affects the performance of the device, which brings great challenges to the micro-machining technology. Based on this, a new terahertz four beam splitter combined with phase coding metamaterials was designed. Only one single-layer metamaterial coding unit can be used to realize the separation of broadband electromagnetic beam and high beam conversion efficiency. The structure of THz beam splitter is simple and easy to process, while the direction of the reflected beam can be flexibly adjusted. In order to match the actual test system, we focused on beam separation at different angles of incidence and obtain the best range of oblique incidence angles (less than 30°). The relative bandwidth is 52%, and the reflected four beam powers differ by no more than 10%. This provides a new solution for the local oscillator signal power distribution of terahertz superconducting mixer array receivers of RF telescope, and also facilitates the design and development of other new terahertz functional devices.