The surface wettability of carbon fiber is an essential factor affecting the performance of carbon fiber composite material.Due to the small fiber diameter and the transparent characteristic of working medium,the con- ventional measurements of wettability need demanding operation whereas wetting boundary is blurred,and thus the reiteration rate of experiment is low and large errors occur.In order to solve this problem,a novel observing method of wettability using IR thermal imaging is proposed.The superficial wettability of carbon fibers with smooth or rough morphology is observed,the variation tendency of wetting height with time is explored,and a comparison is made between the experimental results and the theoretical ones obtained by classical Laplace-Washburn model.The results show that the wetting heights measured in the rapid wetting stage and the transitional stage are respec- tively in direct proportion to the square root of wetting time ( h ∝ 槡 t ) and to the cube root of wetting time ( h ∝ 3 槡 t ),which means that the proposed IR thermal imaging method helps obtain accurate wetting height of carbon fiber tow and can be applied to the characterization of surface wettability of carbon fiber tow.