The influence of core size, relative refractive index difference, stress and bending radius of silicon-based silica waveguides on polarization was analyzed. Conclusions were drawn as below: the birefringence of square waveguide with small relative index difference is small. The birefringence caused by residual stress is larger than that by core size. Small bending radius causes high birefringence and loss, so large bending radius is preferred within the permission of chip size to reduce birefringence.