Abstract: The effects of Si on the electrochemical performance and battery performance of the positive electrolyte of vanadium redox flow battery（VRFB） were studied by cyclic voltammetry,electrochemical impedance spectrum and charge-discharge test.The results indicate that with the content of Si in the electrolyte at 0.03 g/L,the diffusion coefficients of V（IV） species are decreased from（1.43～2.32）×10^-6 cm²/s to（1.23～1.99）×10^-6 cm²/s,and the value of electron transfer resistance is increased from 1.188 Ω·cm² to 1.593 Ω·cm²,resulting in the decrease in both of the electrochemical activity and the reversibility of V（IV）/V（V） reaction of the electrolyte.Meanwhile,the decay rates of capacity and energy of the battery are increased significantly,with the average coulombic efficiency and the average energy efficiency decreased by 1.39% and 3.23%,respectively.