The present disclosure provides a method for forming an active layer with a pattern. The method includes forming an amorphous silicon layer and forming a function layer on the amorphous silicon layer. The function layer has a same pattern as the active layer. The method further includes performing a crystallization process for converting the amorphous silicon layer to a poly-silicon layer. The poly-silicon layer has first portions covered by the function layer and second portions not covered by the function layer, and grain sizes of the poly-silicon in the first portions are larger than grain sizes of the poly-silicon in the second portions.