A broadband terahertz waveguide type beam splitting scheme for multi-port outputs is proposed, which is realized by uniform mode coupling of the multiple subwavelength waveguides. The full-vectorial finite-difference beam propagation method (BPM) is adopted to numerically analyze the mechanism and splitting performance of the beam splitter, and the influence of the supporting structure between the waveguides and the outer dielectric ring on its transmission performance is studied. In particular, a 1 × 8 beam splitter is designed with a coupling zone length of 1.02 mm, which can couple the input THz wave into eight output ports uniformly. The insertion loss of the device is 9.3 dB at the center frequency of 0.54 THz and the bandwidth can reach 0.21 THz with insertion loss lower than 10 dB.