Abstract: According to the philosophy of systematicism，the concept of global function of complex digital systems is proposed．Then a novel approach of test generation is introduced．This approach may be summarized as a two step process．The first is to extract the global function model by topological analysis and logical analysis of the complex digital system，and the next is to find the input vector sequence for verifying this model．These procedures can be accomplished with computer aided tools based on algorithmic graph theory and logic synthesis．This approach facilitates the practical solution of VLSI test generation and is adaptable to digital systems described in different levels of abstraction．