Three-photon absorption coefficient obtained by current nonlinear transmittance method has large fitting error because of uneven laser radiation distribution. Relatively small three-photon absorption cross section values of present nonlinear molecules restrict their practical applications. In this paper, an accurate three-photon absorption coefficient fitting method is presented, which is applicable for a variety of laser distributions. A fluorene-based derivative, 2, 7-bis(4-methoxyphenylacetylene)-9-thoine-fluorene, is synthesized. Apparent three-photon-absorption-induced optical stabilization effect is shown.