Solid surface wettability determination method

A solid surface wettability determination method is disclosed. A liquid is sprayed on a surface of an object. A light beam is projected toward the surface, wherein the light beam is reflected by the liquid on the surface to generate a reflected light. The reflected light is received by an optical detector, and the optical detector outputs a determining signal related to a wettability of the surface according to the reflected light. A corresponding signal-angle relation is selected from a database according to type of the liquid and material of the object. The contact angle of the liquid on the surface is obtained by applying the determining signal to the corresponding signal-angle relation.