The invention provides a miniaturized flat coaxial cavity filter, which mainly solves the problems of complex assembly, high cost and large loss of the current coaxial filter. The miniaturized flat coaxial cavity filter comprises an upper side metal cover plate (1), two feed structures (2), a middle metal inner conductor (3) and a lower side metal cover plate (4). The two feed structures are located on the upper side metal cover plate, and the middle metal inner conductor is clamped between the upper side metal cover plate and the lower side metal cover plate. The upper side metal cover plateis provided with a plurality of upper partition plates (13) and a plurality of tuning screws (12), and the middle metal inner conductor comprises two taps (32), a plurality of resonators (33) and a peripheral fixing part (31) and is of an integrated structure. The lower metal cover plate is provided with a plurality of lower partition plates (41) and a plurality of ridge metal blocks (42), the coupling coefficient is controlled through the upper partition plates and the lower partition plates, and the resonant frequency of the resonators is reduced through the ridge metal blocks. The miniaturized flat coaxial cavity filter is low in loss, low in cost, small in size and easy to process, and can be used for a mobile base station system.