The invention discloses a compact circular waveguide TM01-TE01 mode converter, and aims to provide the mode converter from a circular waveguide TM01 mode to a circular waveguide TE01 mode, wherein the mode converter has a compact structure, and the input and the output of the mode converter are on the same straight line. The mode converter mainly comprises an input circular waveguide (1) for propagating the TM01 mode, an output circular waveguide (5) for propagating the TE01 mode, N rectangular E-surface 90-degree bending waveguides (2), N rectangular 90-degree twisted waveguides (3) and N rectangular H-surface 90-degree bending waveguides (4), wherein N is an even number greater than 3. According to the mode converter, the two circular waveguides for propagating the TM01 mode and the TE01 mode separately are coaxially arranged; the adjacent one surfaces on the inner sides of the two circular waveguides are short-circuit surfaces; the two circular waveguides are in coupling connection through a series of rectangular waveguide assemblies with even-number columns, wherein the rectangular waveguide assemblies are connected in sequence, and the side faces of the rectangular waveguide assemblies are arranged at the equal intervals; the mode converter is compact in structure, small in size and light in weight; the mode converter adopts an axial symmetrical structure, and the input and the output are arranged on the same axial line, so that the mode purity of the output TE01 mode is improved.