Abstract: The hierarchical control structure of multi-lane traffic flow is divided into the coordinated control layer，segment control layer and vehicle control layer.In the paper an optimal control model is proposed for the segment control layer.The objective of the model is to maximize the total traffic flow volume and the average velocity in a segment，and the decision variables are the rates of vehicles’ number in different lanes on the same segment.The number of decision variables in this model is greatly reduced compared with that of traditional linear model.The genetic algorithm，which can overcome the disadvantage of some optimal algorithm that may obtain local optimal solution，is employed to solve the nonlinear program model.The simulation examples demonstrate the effectiveness of the model and its solution algorithm.