The invention provides a multiband miniature directional coupler based on a sharp bent rectangular waveguide for settling a technical problem of positive correlation between size and the number of coupling frequency points in an existing waveguide type directional coupler. The multiband miniature directional coupler comprises the components of two first waveguides, two second waveguides, wherein the two first waveguides and the two second waveguides have E-surface chamfers, a first ultra-transmission metal diaphragm with a composite C-shaped slit, and two second ultra-transmission metal diaphragms. The chamfers of the two waveguides are in butt joint with each other, and furthermore a butt-jointing surface is provided with a first ultra-transmission metal diaphragm. The chamfers of the twosecond waveguides are in butt joint with signal channel ports which are respectively arranged on the end that is next to the chamfer on the large-area H surface of each of the two waveguides, and furthermore the butt-jointing surface is provided with the second ultra-transmission metal diaphragm, thereby finally forming an integral structure which is in mirror symmetry relative to the chamfer ofthe first waveguide. The multiband miniature directional coupler has advantages of realizing directivity and isolation degree, realizing no correlation between volume and the number of coupling frequency points, and realizing miniaturization of the directional coupler on the condition of multiple coupling frequency bands. The multiband miniature directional coupler can be applied to a microwave measuring circuit.