The present invention provides a method for detecting a size of a pattern made by photolithography, which being applied for detecting a size of a pattern formed on an array substrate of a liquid crystal display including: deriving function layer parameters and position parameters of a detection-pattern; deriving a thickness-profile of the detection-pattern according to the function layer parameters and the position parameters of the detection-pattern; deriving a plane-profile of the detection-pattern according to the thickness-profile of the detection-pattern; proceeding a size-detection to the plane-profile of the detection-pattern.