Embodiments of this application provide a dual-mode resonator, a filter, and a radio frequency unit. The dual-mode resonator includes a cavity and a dual-mode dielectric body coupled to an inner surface of the cavity. The dual-mode dielectric body includes a central part and four components that protrude from the central part, where the four components are disposed opposite to each other in pair and are in a cross shape. A first coupling groove and a second coupling groove are provided on the central part, where an extension direction of the first coupling groove is between two adjacent components, and an extension direction of the second coupling groove is between the other two adjacent components. The widths and/or the depths of the first and the second coupling grooves are different, and the extension direction of the first coupling groove and the extension direction of the second coupling groove are at a preset angle.