Work Zones widely exist on highways, causing high traffic delay and many accidents. The majority of the existing studies focus on the characteristics of work zones, such as traffic capacity, speed, delay, queue, etc., while few studies tried to model the traffic flow of work zone. So far, it still lacks the macroscopic traffic flow model for the high work zone. This paper attempts to propose a macroscopic model for the traffic flow in the work zone by dividing the traffic into the two sub-traffic flows, the traffic flow of the occupied lanes and the traffic flow of the unoccupied lanes. The interaction characteristics of the two traffic flow are investigated carefully. Furthermore, the proposed model is also validated using real work zone data. The study finds that the macroscopic traffic flow model proposed in the paper can reflect the traffic characteristics of the work zone with high performance.