Abstract: In the paper, the impedance matching between RF source and antenna load was studied by adopting the three liquid stub tuner for ion cyclotron resonance heating (ICRH) on Tokamak based on the transmission line theory. The impedance matching process was analyzed, and the optimized parameters of three liquid stub tuner for the changeable antenna input impedance were obtained according to impedance matching condition. The numerical simulation results show that optimized parameters of three liquid stub tuner can make the antenna system obtain good matching when the other experimental conditions are same.