The disclosure provides an ultra-wideband non-metal horn antenna, which includes three combinable non-metal elements such as an impedance matching member, a field adjustment member and an outer cover member. The impedance matching member and the field adjustment member are respectively disposed with a first and second groove structures. The field adjustment member is connected between the impedance matching member and the outer cover member. Therefore, the horn antenna of the disclosure can have a more symmetrical radiation pattern, a smaller antenna size, and ultra-wideband performance.