In the photoelectrochemical water splitting reaction system, the bubble will cover the reaction area on the photoelectrode surface, affecting the reaction impedance and gas-liquid mass transfer. A laser irradiation system was built and coupled with an electrochemical workstation and high-speed microscopic imaging system. The evolution behavior and mass transfer characteristics of single O ₂bubble on the TiO ₂photoelectrode were studied at different electrolyte concentrations (Na ₂SO ₄, 0.1-2.0 mol/L). With the increase of electrolyte concentration from 0.1 mol/L to 2.0 mol/L, the solution resistance and bubble additional resistance decrease, and the overpotential in the stable growth stage of bubble decreases from 0.113 V to -0.089 V. The bubble will cause the fluctuation of overpotential in the nucleation, growth and detachment stages, which is consistent with the impedance change caused by the change of dissolved oxygen concentration in the liquid phase. By analyzing the correlation between gas evolution efficiency and bubble coverage, it is found that the increase of electrolyte concentration would lead to the simultaneous decrease of bubble coverage and gas evolution efficiency. By calculating the Sherwood dimensionless number, the results show that the total convective mass transfer coefficient increases with the electrolyte concentration. Single-phase natural convection plays a dominant role in the process of gas product transfer, and its mass transfer coefficient is one order of magnitude larger than that of bubble-induced convection. In summary, by adjusting the electrolyte concentration, the bubble on the gas evolution photoelectrode surface can be effectively removed and the mass transfer of the system can be optimized, which is of great significance for improving the efficiency of photoelectrochemical water splitting.