Based on object oriented timed place Petri net (OOTPN) model, the study on the loading and unloading schedule of automatic Storage/Retrieval System is given. The OOTPN model is established through dividing the model into six sub models according to the class of AS/RS elements, that is: In-Buffer model, In-Plant model, In-Elevator model, Out-Elevator model, Out-Plant model and Out-Buffer model. The six sub models. Furthermore, the deadlock analysis problem of the process is also discussed, and the maximally permissive feedback control strategies for deadlock avoidance are finally proposed.