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.