Ferroelectric material is a kind of material with spontaneous polarization, and water is a common polar solvent. Due to polarity, there are complex interactions at the interface between ferroelectric materials and water/aqueous solutions. Understanding these physical processes and mechanisms is of great significance for both theoretical research and practical applications. Herein, the surface structure of (001) orientated BaTiO ₃with (001) direction polarization single crystal is studied by synchrotron radiation diffraction technology, and the effects of liquids with different pH values on surface structure of BaTiO ₃single crystal was also investigated. The results show that BaTiO ₃single crystal contains a surface layer with a low electron density, and due to the effect of polarity, a 2.6 nm-thick water layer is adsorbed on the surface of BaTiO ₃single crystal. After adding deionized water on the surface, there is no significant change in the surface layer structure of BaTiO ₃. Low temperature in-situgrazing incidence X-ray diffraction experiments indicate the presence of ice on the surface, further confirming the existence of adsorbed water layers on the surface. A hydrochloric acid solution with pH = 1 has no significant effect on the surface structure of BaTiO ₃, either, which is possibly due to the ability of acidic solutions to stabilize the original polarization direction. However, an NaOH solution with a pH = 13 can thicken the surface layer, which possibly results from the weakening of surface polarization caused by alkaline solutions, thereby changing the surface depolarization field and surface layer thickness.