Provided is a method of detecting a defect of a pattern using vectorization to increase accuracy and efficiency in OPC modeling and OPC verification. The method includes acquiring a target layout image associated with a target pattern, acquiring a pattern image associated with a pattern formed on a substrate, extracting an edge image from the pattern image, producing a first vector form based on the target layout image, producing a second vector form based on the edge image, and comparing the first vector form with the second vector form.