The concept of aspect-orientation allows for modularizingcrosscutting concerns as aspect modules. Aspect-orientationoriginally has emerged at the programming level, now it stretches over other development phases such as design phase. Aspect-oriented modeling is important for the aspect-oriented design, since the inaccuracies inherent in aspect-oriented design can be detected by the model, which can help the designers correct the software design.This paper presents a Petri net-based approach to supportaspect-oriented modeling, for Petri net is a good formalism which can provide the foundations for modeling software and simulating its execution. First, software systems are modeled as aspect nets and base net, then woven mechanism is given to compose the aspect netsand base net. There are order constraints and aspect dependencies among the aspects that supposed on the same join point, and there also may exist conflict relations. The above problems are considered in our approach, and a solution is given by analyzing the structure of the woven net to detect such conflicts.