Abstract: At present, when a sequential digital system is synthesized, there is not any systematie method in respect of finding a minimum closed cover of incompletely defined state table. What this paper presents is such a systematic method. First, it is described how to draw an implicit map of MC(maximum compatible) terms. Second, two methods of simplifying the map are given. Finally, applying the catch point's recursive selection and the loop decomposition into simplified map, we are able to find out a minimum closed cover from a set of maximum compatible terms. For a more complex incompletely defined state table this mapping method has more obvious advantage over the try-and-error method applied widely at present.