The utility model relates to the technical field of small size large-power cavity filters, in particularly discloses a small cavity filter suitable for a low-pressure environment. The small cavity filter comprises a cavity body, an inner cover body, a tuning screw and radio frequency connectors, wherein the cavity body is of a box-shaped structure, a plurality of metal cylinders with grooves on the centers are arranged on the inner bottom surface of the cavity body, through holes are arranged on two sides of the cavity body, the two radio frequency connectors are fixed on the through holes at two sides of the cavity body and connected with metal cylinders at two ends in the cavity body through a metal rod, the inner cover board is arranged on the upper end of the cavity body, and the running screw penetrates through the inner cover board and extends into the grooves of the metal cylinders. The small cavity filter adopts a sealant and double-clapboard structure, and overcomes the defect that the cover board and the cavity body directly possibly cause the volume change of the cavity body to cause that electric property changes with the temperature. The small cavity filter has small volume, light weight, excellent electric property, capability of loading high-power input in the low-pressure environment, and excellent stability.