Abstract: Laser surface melting technology can effectively reduce nano optical waveguide sidewall roughness for scattering loss reduction. To clarify the temperature field evolution law of KrF excimer laser surface melting on waveguide sidewall, a two dimensional finite element numerical model is established, which has taken into account the effects of temperature dependences of material parameters and latent heat. Several investigations have been made about the relationships between the carry behavior forward of melting pool boundary and different processing parameters. Simulation results indicate that melting pool begins developing in the corner between the upper surface of waveguide and the laser-facing sidewall surface. At a given laser incidence angle, the depth of melting pool is correlated positively with the average energy density. Melting pool shape is mainly controlled by laser incident angle: with the decreasing incidence angle, the melting pool appears firstly single-edge U-shaped, then single-edge V-shaped, and finally single-edge V-shaped with an obtuse angle. Analysis shows that melting pool shape induced by a larger laser incidence angle is more favourable to the finishing process of waveguide sidewall. On this basis, a new process method is proposed for determinating laser incident angle to optimize the shapes of melting pool and then selecting the appropriate laser energy density to obtain sufficient melting depth.