The correctness of workflow models is one of the major challenges in context of workflow analysis. The aim of this paper is to provide an improved Petri-net-based reduction approach for verifying the correctness of workflow models. To the end, how to represent well-behaved building blocks and control structures of business processes by Petri nets is given at first, and then how to build well-structured process nets is presented. According to the structural characteristics of well-structured process nets, a set of legacy reduction rules are improved and extended, and then a complete Petri-net-based verification approach is proposed. The soundness and the complexity with polynomial time for the improved reduction method are also proven.