A planning method for power metal lines is provided. The planning method includes selecting a block to plan, the block including a first metal layer and a second metal layer therebelow. The first metal layer includes a plurality of first metal lines along a first direction and the second metal layer includes a plurality of second metal lines along a second direction. The block includes a length in the first direction and a width in the second direction. According to a ratio of the length and the width of the block, a line width adjustment procedure is performed to adjust a first line width of each of the first metal lines and a second line width of each of the second metal lines, so that routing congestion can be avoided without affecting the IR drop.