Parallelizing restructuring has become an essential means to exploit the vast computing power of modern supercomputers．But many parallelizing restructuring systems ignore or simplify the interprocedural data—flow analysis，so they can not transform a do—loop which contains call statements into parallel code．This thesis introduces a practical interprocedual data—flow analysis in the front—end of the parallelizing optimizing restruc-turing tools(PORT)，which was developed at the Institute of Computing Technology，The Chinese Academy of Sciences．It concentrates on the interprocedual data—flow analysis’s idea．key techniques and application．