Abstract: Air flow bifurcations often occur ina room with mechanical ventilation system, and will change the velocity andtemperature fields in the room. The main influencing factors of air flow bifurcationsin rooms with mechanical ventilation system are studied in this paper.First, with the jet theory and the results of computer simulation, thepaper explains why bifurcation occurs with plane jet but not with centralized jetby analyzing Coanda effect. It is shown that Coanda effectis the main mechanism of bifurcation. Second, the key parametersaffecting bifurcations are analyzed using the theory of orthogonal test andvariance analysis. The relations between bifurcation intensity and thekey factors are obtained.