Abstract: In order to solve the problem of detectors layout space under different traffic operational states, a piecewise function model of flow-occupancy was presented theoretically and estimated by using the surveyed data, considering both traffic operational states and applicability of traffic flow models. Under the high and low occupancy states, combined the principle of traffic incident detection with traffic wave propagation model, the occupancy after the event was determined by the simulation method and the theoretical values of the detectors layout space were suggested on the basis of the flow-occupancy model. The detection response time of the event was supposed to be 1min, the detectors distance was 1.0km under the low occupancy, and the detector distance was 0.5km under the high occupancy.