This paper proposes a new system modeling approach about Grey Structural Modeling (GSM) which is based on grey theory, and it just likes ISM and FSM. Each class of systems depends on the order of localized grey relational grade. And each path of elements is found by the ordered pair of according to globalized grey relational grade. Classes and paths are both used Yamaguchi's grey relational grade, since it is more suitable to find the topology of given elements. GSM draws directed graph (digraph) by using three parameters: distinguish coefficient ζ which decides the basic composition of digraph, class coefficient θ which gives the hierarchy, and path coefficient ψ which gives an ordered pair of elements arrow. It is possible that the GSM handles not only causal binary relation, but also observed value which causality is unknown. Three examples are given, proposal method is analyzed and compared with traditional methods.