Abstract: This paper points out that the Gongcheng Zuofa, Yingzao Suanli, Qingshi Yingzao Zeli are three different construction treatises, and the confusion of the three caused several concrete fallacies. On this basis, returning to the original text of Gongcheng Zuofa, it reexamines the concept or question of system of bracket modular (doukou), overhanging (cai), bay (jian), lift of flying rafter (fuyanchuan jujia), extension of hipped roof (tuishan) and contraction of half-gables roof in depth (shoushan), reveals their relationship with Gongcheng Zuofa, and corrects some misunderstandings existing in academia.