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Coordinated multi-ramp control at freeway entrance is to regulate the traffic volume entering into freeway mainlines from all on-ramps. Thus, mainline traffic flow is at its best. The coordinated multi-ramp control system is a strong coupling, nonlinear, and time-varying system because of the interaction of multi-ramps. Aiming at the problems as mentioned above, a coordinated control method is proposed based on a system hierarchy and a particle swarm optimization algorithm. Firstly, the principle and model of freeway multi-ramp system are dissertated. Then, the realization of a coordinated multi-ramp control system is expounded. This control system is composed of a coordination control layer and a direct control layer. Coordination control layer is used to select traffic models, to adjust the model parameters, and to determine desired trajectories of traffic densities. The direct control layer is responsible for control implementation by using proportional-integral-derivative controllers. A particle swarm algorithm is utilized for optimizing the proportional coefficients, integral coefficients, and derivative coefficients. Finally, simulation experiments are carried out. Simulation results show that the control system can quickly eliminate traffic jams and can stabilize the mainline traffic flow when freeway traffic congestion occurs. This approach provides a new and practical way for freeway coordinated multi-ramp control.