A design method of a shuttle mask including the following steps is provided. A first integrated circuit (IC) design is provided in a first chip region, and a second IC design is provided in a second chip region. The first IC design includes first main patterns. The second IC design includes second main patterns. First dummy insertion patterns are added in the first chip region, and second dummy insertion patterns are added in the second chip region. The first main patterns and the first dummy insertion patterns are separated from each other. The first dummy insertion patterns are patterns formed by duplicating at least one of the first main patterns. The second main patterns and the second dummy insertion patterns are separated from each other. The second dummy insertion patterns are patterns formed by duplicating at least one of the second main patterns.