The tradition of using a center pen originated from seal script, because when writing seal script, it is required to use a center pen, that is, the thickness of the strokes is uniform, and only the center stroke can be written. The circle paintings in seal scripts are mostly round and have no square folds. The roundness, thinness and straightness are the basic aesthetic characteristics. Therefore, the central pen has become an indispensable part of the art of calligraphy and continues to this day.