A kind of beam-splitting polarizing filter based on two-dimensional photonics crystal was proposed.The photonic bandgap was calculated by plane wave expansion method to confirm the micro-structure parameters,with which single polarized beam in 1550nm can be obtained;Finite-different time-domain method was used to optimize the 90° bending buffer layer and impacting wall of beam-splitter.This device indeed is a waveguide fabricated by introducing defect in two-dimensional photonics crystal array,a single polarization source can be obtained by using photonics band gap and 90° linear defect to filter a certain polarization completely off.By the construction of Y-shaped defect,an approximate splitting ration of 1: 1 is achieved.Through the optimization of the 90° linear defect and buffer layer,a ratio of 68% between the output power and input power is finally gained.