Abstract: In view of the low efficiency of on-board hydrogen generator used in the vehicle with hydrogen-blended gasoline engine due to adding metal ions in water, effects of different concentration of Zn ²⁺, Fe ³⁺ and Cu ²⁺ on performance of the on-board hydrogen generator with KOH liquor were tested on hydrogen generator testing bench in this paper. The experiment was carried out at the electrolytic current of 30A, the initial temperature of 19.7℃ and the pressure of 0.1MPa. The effect of adding 50mL metal ions liquor to the 2L KOH liquor which has a KOH mass fraction of 30% was investigated and compared with the pure KOH liquor electrolyzing. Results show that the electrolytic voltage is increased, and the hydrogen producing velocity and efficiency are reduced with the increase of metal ions concentration.