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In response to the new requirements of cognitive radio technology for radio frequency microwave filters, an electronically tunable microwave filter based on stub-loaded multi-mode resonators is proposed. The electronically tunable microwave microwave filter is composed of a stub-loaded microstrip multi-mode resonator and varactor diodes, which realizes the miniaturization of the filter. Based on the analysis of the stub-loaded microstrip resonator, a stub-loaded electronically tunable microwave multimode microstrip resonator was designed by loading varactor diodes on both ends of the microstrip resonator and the loading stub, and an analysis method of resonance characteristics of complex microstrip resonator is proposed. A transmission zero is introduced to the right of the passband by means of source and load coupling. The passband selectivity of the filter is improved by placing coupled lines at the source and load ends. Aiming at the problem of small out-of-band attenuation of the filter, a new type of frequency-dependent feed structure is introduced to improve the out-of-band attenuation of the filter. The size parameters of the electronically tunable microwave filter are determined by optimization simulation. The characteristics of the filter are verified by simulation. When the adjustable range of the varactor diode is 2pf-10pf, the frequency adjustable range of the filter is 2.10GHz-2.40GHz, and the frequency change range is 300MHz.