The invention discloses a high-power coaxial fixed attenuator which mainly comprises an SMA (shape memory alloy) female joint, an SMA male joint and an attenuator cavity. The cavity comprises radiators, two core cavities, two attenuation slices, ground clamps and a connector; the male joint comprises a swivel nut, a clamp ring, a male shell, an insulator, a male inner conductor, a spring and a contact cap; the female joint comprises a female shell, a female inner conductor, an insulator, a spring and a contact cap; and the connector comprises a connector inner conductor, a connector shell, an insulator, a spring and a contact cap. Metal oxide is used as a substrate, and an advanced resistance technology is adopted, so that the high-power coaxial fixed attenuator is high in the power density and stable in resistance. Besides, owing to the optimally designed card-shaped attenuation slices, requirements on small standing waves and wide frequency band are met. In addition, the working frequency of the product ranges from frequency of direct current to 26.5GHz, the power capacity of the attenuator is 50W, and the high-power coaxial fixed attenuator has good and quick radiating ability and is high in burning resistance and good in mechanical stability and repeatability.