This paper presents a file format for Gong-che Notation(GCN, a Chinese musical notation). It firstly describes basic knowledge of GCN, and indicates the differences and similarities between GCN and WMN(Western Music Notation), then we put forward the file format of SMIDI(Similar Musical Instrument Digital Interface) of CGCN(Code of GCN), and a software interface of SMIDI of CGCN. The file format is strong of compatibility, robustness and fault tolerance, it realizes GCN score and its digital musical information synchronous transmission, and effectively solves the ambiguous problem for translating from GCN score to WMN score, and makes the Chinese traditional music works to reuse and communication in digital era.