Based on 100 nm GaN-on-Si MMIC technology, this paper presents the design of a 20-26 GHz Variable-Gain Low-Noise Amplifier (VGLNA).This LNA adopts a three-stage common source topology and realizes gain control by adjusting the gate bias of the second and third stages.The test results show that the amplifier achieves a >20 dB gain tuning range and a ±1.5 dB gain flatness within the working frequency range, and dissipates power from 126 mW to 413 mW.When biased with a -1.1 V gate voltage and 3.5 V drain voltage, the amplifier achieves a small-signal gain of more than 20 dB in the whole band, a Noise Figure (NF) ranging from 2.95 dB to 3.5 dB, and an average output 1dB compression point(OP1dB) around 14.5 dBm.The chip area is 2 mm².