Slicing is a well-known reduction technique．Most of the research on slicing is code-based．There has been limited research on specification-based slicing and model-based slicing．EFSM is a very important specification model，but a practical EFSM model is often large and complex and is hard to understand and modify．EFSM—based slicing is very useful to test and analysis EFSM models．The dependence analysis based EFSM dependence graph is much more than a graph reachability problem，so that traverse algorithms based marking visited nodes carl not to be used in EFSM dependence graphs．In this paper,we discuss dependence analysis in EFSMs，and define a dependence transform function and a reverse dependence transfer function to describe dependence transform formally．Based the analysis and defmition，a backward slicing algorithm is given to find all transitions which may affect an interesting transition．