simple and effective method for calculating the scattering from a point defect (like an air bubble or a dust grain) in a planar waveguide is presented. The method is based on the theory of Green′s function. To improve the calculation efficiency,the corresponding integral equation is converted into a matrix equation by using the method of moment and the method of blocked matrix is also used. A silica planar waveguide is considered as an example;the scattering loss as a function of the size of the point defect is analyzed for both an air bubble and a dust grain. The results indicate that the scattering loss depends on the size of the defect and optical property rather than its situation in the waveguide. It is also shown that a point defect of a certain size may cause some strong resonances at some special wavelengths and will result in a large scattering loss. For the same reason, point defects with some special sizes should be avoided in the fabrication in order to reduce the scattering loss at an optical communication wavelength windows