Abstract: Routine calling between codes written in different languages is a useful skill, which allows programmer make better use of existing software resources.This paper investigates an interfacing method between C and Fortran in VAX/VMS environment. The disscussion is based on the author’s experience on calling VAX/RGL from the C applications. The key is to flat the gap between the VAX routine parameter passing mechanism in these two languages. Also introduced is a C interface software for RGL, which is implemented by the author according to this method.