Worldwide concern has been focused on the airborne disease of the COVID-19 pandemic. This study investigated the effect of the limited space air stability on the mechanism of SARS-CoV-2 spreading in the interpersonal breathing microenvironment using an unsteady computational fluid dynamics (CFD) method. A validated numerical model was employed to simulate the transient SARS-CoV-2 releasing process from normal breathing activity. The computational domain was divided into an interpersonal breathing microenvironment and the rest macroenvironment. A displacement ventilation system was implemented with 1.5 ACH, 3 ACH, 7.4 ACH and 9 ACH. Two standing CSPs (Computational Simulated Person) were placed in the middle of the macroenvironment face-to-face with a relative distance of 1 m. Simulation results indicated that in stable cases, the exhaled SARS-CoV-2 tended to accumulate in the interpersonal breathing microenvironment and resulted in a relatively high infection risk for people; whereas in cases where unstable air presented, SARS-CoV-2 concentration was significantly reduced. The unstable conditions lowered the risk of person-to-person transmission in confined spaces. Also, it was found that unstable cases performed better in energy efficiency in comparison with the stable conditions.