This letter reports a high-precision wave measurement system for accurately determining the velocity of leaky Lamb wave. For an X-cut LiNbO3 plate, the change in leaky Lamb wave velocity induced by fluid’s dielectric loading effect has been measured. The measured correlation between fluid’s permittivity and induced wave velocity variation has been compared with theoretical results obtained form partial wave theory. Good agreements are observed. Potential applications of this wave measurement system are addressed.