A mask for laser-crystallizing amorphous silicon into polysilicon is provided. The mask comprises a transparent substrate having a first block, a second block, and a third block with equal sizes. The second block is located between the first block and the third block. The first block includes a plurality of first transmission regions and a plurality of first opaque regions located between the first transmission regions. The second block includes a plurality of second transmission regions correspond to the first opaque regions and a plurality of second opaque regions located between the second transmission regions and corresponds to the first transmission regions. The third block includes a plurality of third transmission regions arranged corresponding to the centers of the first transmission regions and corresponding to centers of the second transmission regions and a plurality of third opaque regions located between the third transmission regions.