The paper introduces a new delay detection method based on the video double section trigger.Two virtual detectors were set to record the vehicles’ arrival and departure information.Upon the vehicles’ arrival of the intersection,the vehicles blobs were extracted to be tested whether the blobs could be matched.If the blobs could be matched for eight times successively,the new vehicle was thus detected.A real time tracking by the vehicle’s stain and meanshift algorithm would not stop until it departed,and parameters of delay were obtained.With the proposed method,over 90% of delay and more than 95% of the traffic flow precision can be detected on real time.