To complement the weakness of Petri nets in terms of naturalness, modularity, and reusability, high-level Petri nets with object concepts have been suggested. It is difficult to apply these nets to the requirements specification of object-oriented software systems because of insufficient support for the object-oriented concepts. A hierarchical object-oriented Petri net (HOONet) is developed to complement the weakness of the existing formalisms and formally define its syntax and semantics. A reachability analysis method is provided to check such behavioural properties as boundedness, liveness and persistence of the HOONet models. The HOONet provides incremental modelling and analysis of the requirements with the support of object-oriented concepts.