This paper introduces the research and design of the tunable filter based on the GaAs varactor technology, including the preparation of the variable capacitance material, the establishment of the diode model and the circuit design. Several tunable filters are designed, and the frequency range covers 1-19 GHz. The test results show that the tunable filter has more than one frequency doubling range, the breakdown voltage of the device is greater than 30 V. In this paper, a tunable filter with central frequency 2-5 GHz adjustable is introduced in detail. The control voltage range is 0-15 V, the insertion loss is about 10 dBm, and the input and output return VSWR(Voltage Standing Wave Ratio) are better than 1.8. The series of tunable filters designed bear the advantages of high consistency, miniaturization, low cost and debugging-free, and have good application prospects.