The invention discloses an ultra-wideband monopole antenna. The antenna comprises a monopole, a metal floor and a feed pin. The feed pin is connected to the monopole through the metal floor, and a circular gap is arranged on the metal floor with the feed pin as a center. The monopole is arranged above the metal floor, and is composed of two metal cylinders vertically connected and having differentdiameters, and the diameter of the upper part cylinder is larger than that of the lower part cylinder; the outer periphery of the axial section of the monopole is in the shape of a rectangular ladder. Compared with the existing monopole, the antenna impedance bandwidth of the stepped cylindrical monopole is obviously improved, and can cover an UWB frequency band range. The design of the metal floor can increase the antenna radiation intensity. There are many kinds of feeding structures to meet the needs of different applications. The operating frequency band covers 3.1 GHz-10.6 GHz, the frequency band is suitable for an ultra-wideband (UWB) communication system, suitable for a wide-range popularization and application, the voltage standing wave ratio (VSWR) is less than 2, and a reflection coefficient is less than 0.3.