The crystallization behavior of amorphous silicon is affected by direction and intensity of electric field in FALC（Field-Aided Lateral Crystallization). Electric field was calculated in a simplified model using conductivity data of Mo, a-Si, $SiO_2$and boundary conditions for electric potential at the electrodes. The magnitude of electric field intensity in each corner of cathode was much larger than that in the center of patterns, and the electric field direction was 50~60 degree outside to cathode. And electric field intensity at a relatively small pattern was larger than that of a large pattern.