A delay diagnosis method is proposed that can avoid design steps from being retraced or repeated uselessly due to defective delay when we design a semiconductor integrated circuit including a plurality of blocks. This delay diagnosis method has the steps of inputting logic information and floor plan information, finding the number of start points connected to the end point of a path from the logic information, computing the logic stage number of the path from the number of start points, finding block-to-block distances from the floor plan information, computing intra-block delays from the logic stage number and gate unit-value delays, computing inter-block delays from the block-to-block distances and routing unit-value delays, and diagnosing if the delay of the path after logic synthesis can be converged within a target path delay from the relation among the computed intra-block delays and inter-block delays and the target path delay.