Abstract: The advantages to poly silicon film instead of amorphous silicon film in the field of flat panel display were introduced. Crystallization process of poly silicon film by using excimer laser crystallization system was studied. The principle of how lens array achieve the uniformity of output laser energy density was described. The structure of typical excimer laser annealing(ELA) line beam shaping system, which included beam expanding unit, beam energy homogenizing unit, projection unit and so on was focused on. Finally the application of sequential lateral solidification technology in the area of low temperature poly silicon(LTPS) using excimer laser nnealing was introduced. The status of ELA optical system was discussed and its significance in flat panel display industry was pointed out.