The present invention provides a pattern verifying method. First, a target pattern is decomposed into a first pattern and a second pattern. A first OPC process is performed for the first pattern to form a first revised pattern, and a second OPC process is performed for the second pattern to form a second revised pattern. An inspection process is performed, wherein the inspection process comprises an after mask inspection (AMI) process, which comprises considering the target pattern, the first pattern and the second pattern.