The invention discloses a method for measuring and calculating the queuing length caused by traffic accidents on the urban road based on fixed detectors and relates to a method for calculating the queuing length caused by the traffic accidents according to the fixed detectors arranged on road sections after the traffic accidents on the urban road occur. The method comprises the following steps of: calculating the arrival rate of vehicles on an entrance way at a crossed port; detecting the leaving rate of the vehicle at the crossed port; calculating the queuing length based on the fixed detector; and finally determining the maximum queuing length. By using the invention, the aim for quickly and accurately obtaining the queuing length for jam caused by the traffic accidents on the urban road can be achieved. The method has high accuracy and is simple and practical.