Almost all optical materials have the properties of thermal refractive index varying. Under the action of the local thermal source, distribution of refractive index is gradient, and the direction of propergation of the passing light beam will deflect. According to this physical property, it is possible to make various thermo-optic devices. It is proposed to fabricate strip Ti-film thermal source and to measure the deflecting angles of emergence beam in the paper. Using analytic method, the distribution of refractive index on the profile of substrate is obtained. An then according to energy conservation, tempreture coefficient of refractive index of the material is obtained. Compared with the annouced values, it is verified that our experiment method is correct. The method described is available for studying and analying thermo-optic materials and devices.