The method of integrating many partial simulators for a complicated system in the consideration of interaction is proposed. Java Native Interface is used to integrate the simulators programmed in different languages. Remote Method Invocation is used to integrate the simulators in different computer environment. By applying the method to the partial simulators on the blast furnace, java-based integrating simulator for the blast furnace is constructed in order to support the operation of operator. Developing the simulator by the method can save considerable labour and decrease time consumption greatly than redeveloping. Furthermore, the visualization system comparing both the simulation results and the actual measurement data is reported.