1. A virtual production control method for effectively conjecturing delivery capability of a real factory at a supplier side, the virtual production control method comprising: processing a current shipping plan and a plurality of sets of historical WIP (Work-In-Process) data respectively belonging to a plurality of historical production cycles sent from the supplier side, thereby obtaining a plurality of historical input schedules and a plurality of historical output schedules belonging to said historical production cycles, an expected production capacity limit of a next production cycle following said historical production cycles, and an loss rate of the most recent one of said historical production cycles; performing an integer programming method by a computer using said current shipping plan and one of said historical input schedules belonging to the most recent one of said historical production cycles, to compute a latest ideal input schedule and a latest ideal output schedule belonging to said next production cycle; and simulating and obtaining a latest feasible input schedule and a latest feasible output schedule belonging to said next production cycle by using said historical input schedules, said historical output schedules, and said latest ideal output schedule belonging to said next production cycle in accordance with a distributed-parameters estimation method, a neural network method and Petri Nets.