Visual programming of the bscas ( bridge structure constructional analysis system ) is realized , the mechanism of establishment and discretization of diagrammatic drawing of bridge structure has been analyzed in details with the theory of mechanics and finite element method . at the same time , theory , function and applicability of the program have also been discussed in the paper 编制了bscas大跨度桥梁结构施工分析软件,从力学和有限单元法原理对桥梁结构计算图式的建立和结构离散化原理做了较为详尽的剖析,对程序的编制原理、功能以及适用范围做了详细的说明和讨论,提出了一些自己的认识和观点。