With the ever increasing computational power of computers and developments in commercial software, reliability of Computational Fluid Dynamics (CFD) simulation in predicting and designing indoor air flows have been improved. This paper presents a new two-way simulation method to demonstrate the solution multiplicity characteristics of indoor air flow. A simple two-zone model with four openings is used to illustrate its application. Numerical simulation results show that the two-way simulation approach can perform well for multiple steady solutions problem. Two steady solutions with the same boundary conditions and building geometry can be identified step by step in the simulation process. The characteristics and behavior of the air flow as the building configuration changes can also be identified. These data can be valuable information for advanced building design purpose. Comparing with conventional CFD simulation, this method can effectively identify the possible existence of multiple solutions of indoor air flows with different initial conditions.