SiO2-TiO2 planar waveguides on Si/SiO2 substrate were prepared by sol-gel method. A fiber laser was used to fabricate strip optical waveguides in the core layer of the planar waveguides by laser direct writing of the sol-gel coatings. The thresholds of laser power density for laser direct writing optical waveguides on the SiO2-TiO2 planar waveguides were studied systematically. Moreover, the relationships between the thresholds of laser power density and anneal temperature on sol-gel films were also discussed. The experimental results show that there are initial shrinkage threshold and damage threshold when laser direct writing strip optical waveguides on the SiO2-TiO2 coatings are fabricated by sol-gel technique. Both the two thresholds mentioned above increase with the anneal temperature on films respectively, but the increasing trend of the damage threshold is more prominent than that of the shrinkage threshold, which indicates a much smaller laser spot allowed in laser direct writing. Therefore, narrower strip optical waveguides in width can be fabricated in this situation. At last, the light propagation character of the strip waveguides was measured, the three-dimensional light propagation mode of the strip waveguides was confirmed.