The invention discloses a rectangular waveguide TE10 mode-circular waveguide TE01 mode converter, which belongs to the technical field of microwave and millimeter wave transmission devices. The rectangular waveguide TE10 mode-circular waveguide TE01 mode converter comprises a rectangular waveguide power division network, a quadrupole waveguide TE01 mode conversion structure and a quadrupole waveguide-circular waveguide transition structure, wherein the TE10 mode inputted by a standard rectangular waveguide is divided into four equal-amplitude TE10 modes through a rectangular waveguide power divider network, the four TE10 modes are injected to the quadrupole waveguide TE01 mode conversion structure at the same time to excite corresponding TE01 modes, and finally, the TE01 modes in the quadrupole waveguide TE01 mode conversion structure gradually change to circular waveguide TE01 modes through the quadrupole waveguide-circular waveguide transition structure, and conversion from the rectangular waveguide TE10 mode to the circular waveguide TE01 mode is realized. Generation of a parasitic mode can be effectively suppressed, the whole mode converter has the advantages of high efficiency, high purity and wide band, and besides, the waveguide mode converter has a compact and simple structure, processing and assembling are easy, and the engineering practicality is good.