A method of correcting a mask pattern is described. A testing mask including a plurality of original patterns configured according to an original drawing data is provided. The original patterns in the testing mask are transferred to a photo-resistant layer to form a plurality of first post-development patterns and measure first dimensions of the first post-development patterns. A pattern shrink process is performed on the first post-development patterns to form a plurality of first post-shrink patterns and measure second dimensions of the first post-shrink patterns. The bias of each the first dimensions and the second dimensions are calculated. The original drawing data, the first sizes, the second sizes and the bias are collected to set a database. The data of the database is used to establish an optical proximity correction (OPC) model. According to the OPC model, an original drawing data is corrected to obtain a corrected drawing data.