Abstract: The in-situ and real-time high-precision measurement of the composition and dynamic change of elements or ions (charges) at the solid-liquid interface with nano-to-micron thickness is very important in the understanding of the interface interaction and reaction, while traditional high-resolution ion beam analysis can not directly measure liquid samples in vacuum environment. In this paper, a solid-liquid interface probe in vacuum was developed. The probe used Si₃N₄-Al nanocomposite membrane as vacuum sealing window and electrochemical electrode. The Rutherford Backscattering Spectroscopy (RBS) analysis and particle-induced X-ray Emission (PIXE) analysis with the solid-liquid interface probes of 0.01 mol/L BaCl₂ and 1 mol/L LaCl₃ solution were successfully carried out using Fudan University nuclear microprobe. The experimental results show that the nano-window of solid-liquid interface probe can withstand the irradiation of 2 MeV He⁺ ions with a dose of 1.0×10¹⁸ ions/cm² in vacuum. The distribution of structure elements in solid-liquid interface probes was successfully obtained by PIXE analysis. The concentration of La and Cl in micron deep solution of electrode interface was obtained by Rutherford backscattering analysis with 20-nm-resolution. On the surface of 1 mol/L LaCl₃ solid-liquid interface electrode, electrolyte ions accumulated at a high concentration at negative voltage (–2.3 V), while electrolyte ions distributed at a low concentration at positive voltage (+2.3 V), and electrolyte solutions tended to bulk concentration at a depth of about 1 250 nm.