The invention provides a high-power-dividing-ratio broadband power divider based on a three-wire coupling structure, and aims to solve the technical problem of low power dividing ratio of an existing broadband power divider. The broadband power divider comprises a dielectric substrate, a floor, a main branch knot, a first branch knot and a second branch knot, the floor is printed on the lower surface of the dielectric substrate, the upper surface of the dielectric substrate comprises a main branch knot, the first branch knot and the second branch knot, the main branch knot is of a two-step gradually-varied micro-strip structure, the first branch knot comprises a parallel short-circuit three-wire coupling transmission line, the tails of three transmission lines in the coupling transmission line are provided with metal through holes, the second branch knot is of a three-step gradually-varied micro-strip structure, and the first branch knot and the second branch knot are connected with the main branch knot through a T-shaped micro-strip knot. According to the broadband power divider, high-power-dividing-ratio characteristics are achieved on the premise of ensuring a broadband.