Abstract: This paper employs the process describingmethod to reveal the confluence movementofthe mixed traffic flow, obtaining that the mixed traffic flow unnecessarily obeys the rule-“the first arrived is served first”-in confluence process. Using the confluence acceptance probability theory, it is obtained that the same acceptance gap has different confluent probability for different vehicle types under mixed traffic flow, and so the space waste of acceptance gaps is produced. Meanwhile, the theories that the confluence area length and the driveway designing have effects on the service level and capacity of high-class highways, and that the confluence area is the watershed and the abrupt change area of the service level of the highways are explained by computer simulation.