We propose a real-time detection method for vehicle queue length detection at intersections based on image processing technology. Firstly, we acquire the image of vehicle queue at the intersection, and apply the automatic brightness adjustment algorithm and lane line detection algorithm to reduce the affect of different light intensity and camera shake on the image respectively. And then, the preprocessed image is subtracted from the background image to obtain the foreground image of queue vehicle. Finally, we detect the vehicle queue length by the middle line, and the actual vehicle queue length is measured by the camera calibration method. The experimental results show that the proposed method has high accuracy rate and is fast enough for practical application.