The invention discloses a waveguide multi-path power distributor/synthesizer applicable to a millimeter wave frequency high end. A fan-shaped waveguide-based power distributor/synthesizer comprises a rectangular waveguide input port, a mode exciter, a 180-degree fan-shaped waveguide, a matching structure and a plurality of (n is greater than or equal to 2) rectangular waveguide output ports, wherein a TE10 mode in the rectangular waveguide excites a TE01 mode in the fan-shaped waveguide through a mode converter (a rectangular waveguide feed source or a Y-type waveguide feed source, the rectangular waveguide feed source is used when the fan angle is smaller than 90 degrees, and the Y-type waveguide feed source is used when the fan angle is between 90 degrees and 180 degrees), and achieves inhibition on other modes. Mode conversion and energy distribution of the fan-shaped waveguide to the TE10 modes of n rectangular waveguides are achieved through the multi-path power distributor; and a signal of each output port is equal in amplitude and phase. Compared with a round waveguide, the fan-shaped waveguide excitation mode is free of polarization degeneracy, higher in mode purity and higher in bandwidth; and compared with a TEM mode with a coaxial line, the fan-shaped waveguide excitation mode is smaller in loss, higher in power capacity, larger in circuit dimension and lower in processing cost and processing difficulty.