A method for manufacturing polysilicon layer is provided. At first, a substrate is provided. An amorphous silicon layer having a second region and a first region is formed on the substrate. The first region is thicker than the second region. The amorphous silicon layer is completely melted to form a melted amorphous silicon layer having a first melted region and a second melted region. The temperature of the bottom center of the first melted region is lower than that of the second melted region and that of the top of the first melted region. The melted amorphous silicon layer is crystallized to form a polysilicon layer. The crystallization begins from the bottom center of the first melted region to the second melted region and the top of the first melted region.