The invention discloses a dielectric three-mode filter based on capacitance loading and slot coupling. The filter comprises a dielectric three-mode resonator, a first coupling slot, a second couplingslot, an input feed port and an output feed port; a rectangular metal box is taken as the outer wall of the dielectric three-mode resonator, a metal column is arranged in the center of the bottom of the metal box, a dielectric block with a through hole is installed inside the metal box, the metal box is accommodated in the through hole, the bottom of the dielectric block is in short-circuit connection with the metal box, and a metal disk is arranged on the top of the dielectric block; the first and second coupling grooves are formed in the metal disk and located in different positions; the input feed port and the output feed port are perpendicularly formed in the two adjacent outer side walls of the metal box, and the input feed port and the output feed port are formed by SMA joints with metal probes connected with coupling metal sheets. The filter has the advantages of being high in Q value, high in power capacity, low in profile, small in size and convenient to perform plane layout design and processing, and the filter is suitable for massive industrial production.