In order to solve the problem of low efficiency of flowchart drawing and better guarantee the consistency of software model, document and code, an algorithm for automatic generation of flowchart was proposed. Firstly, by analyzing the C/C++ source code in reverse, the Token list of the code was extracted, and the Scope tree was created to realize the flowchart generation. At the same time, a method for regulating the annotation of code functions was proposed, improving the comprehensibility of the flowchart. Finally, the readable flowchart was generated after the automatic layout of flowchart by applying the Sugiyama layout algorithm and completing and improving the coordinate designation step. In the actual application process, with the use of the proposed algorithm, the efficiency of writing software design documents is effectively improved and the consistency of the software model, document and code is guaranteed.