The study leverages the three-dimensional Macroscopic Fundamental Diagram (3D MFD) model for urban road networks and constructs a refined 3D MFD model utilizing the actual movement trajectory data of diverse vehicles within the experimental region. The boundary control strategy for mixed traffic flow within the designated control area is developed. This strategy involves determining the traffic flow balance model of the road network through the boundary control process. Additionally, a Proportional-Integral (PI) controller is designed based on the feedback control model of the road network's boundary. The primary control objectives for the boundary management of mixed traffic flows are societal vehicles, with no restrictions imposed on the entry of public transportation vehicles into the controlled zones. The weight assigned to public transport vehicles in the control decision-making process is determined by allocating the proportion of mixed traffic flow at the boundary intersection that enters the controlled area. The efficacy of the proposed control strategy is evaluated through simulation experiments, comparing its performance against existing methods.