This paper analyzes the basic principle of Y-type waveguide splitter, and then designs a terahertz waveguide splitter based on PBG structure using the principle of photonic crystal band-gap. The operating frequency band is 480GHz-520GHz. Simulation results show that the VS WR is less than 1.3 in the operating frequency range, the S parameters of the input port and the output port are nearly 3.08dB and the difference of the two ports is less than 0.1dB, the phase of two output ports is approximately the same in the whole frequency band. In general, this new designed terahertz PBG splitter has excellent performance to meet the needs of engineering applications. The novel THz splitter device can be processed in MEMS deep reactive etching technology.