The invention provides a small-size wideband circularly-polarized feeding source applicable to Mars exploration, and relates to the technical field of a microwave antenna. The small-size wideband circularly-polarized feeding source comprises a feeding waveguide, a circular polarization device, a built-in medium and a horn radiation segment, wherein the feeding waveguide is of a cuboid structure, the circular polarization device is axially, vertically and fixedly arranged at a lower surface of the feeding waveguide, the horn radiation segment is of a hollow cylindrical structure and is axially,vertically and fixedly arranged at a lower surface of the feeding waveguide, the horn radiation segment sleeves an outer wall of the circular polarization device, the circular polarization device isfilled with the built-in medium, a cylindrical groove is formed in the feeding waveguide, an opening direction of the groove vertically faces downwards, and communication between the feeding waveguideand the circular polarization is achieved. The invention provides a single-fed reflecting-surface wideband feeding source, which is compact in size and is used for preventing Mars dust from entering,applicable to Mars landing detection.