Being a kind of restricted intelligent objects, agent is a natural way to research the inheritance feature of software agent and integrate inheritance mechanisms into AOP (agent-oriented programming). Based on BDI model of agents, the semantics of inheritance and cloning behavior of agents are addressed in this paper. The semantics of inheritance are discussed from two aspects: single inheritance and multiple inheritance. For cloning behavior, the authors identify and formally classify the dynamic cloning mechanisms of agent instances into four types: function split, logic split, preference split and retrogress split. The principle of each cloning mechanism is presented and the examples are provided based on the electrical commerce systems.