The invention relates to a method and a system for abnormal target detection and relay tracking under a large-range monitoring scene. The system comprises a target detection module, a target identification and tracking control module and an active tracking module, wherein the target detection module is used for carrying out Gaussian background modeling by utilizing a sub-sampled image to obtain aforeground image, computing the coordinate of a target in a digital map and then sending coordinate information to the target identification and tracking control module; the target identification andtracking control module is used for finishing the target tracking, the track recording and the abnormal behavior detection of the target, and if abnormal behavior occurs, a proper pan-tilt video camera is selected according to the coordinate information of the target, and an alarm signal is sent to the active tracking module; and the active tracking module is used for receiving the alarm information of the target identification and tracking control module, controlling the pan-tilt video camera to carry out preset position steering according to the content of the alarm information and then carrying out the detection and the tracking of the moving target. The invention solves the integration problem of multiple paths of image target information under the large-range monitoring scene and realizes the accurate and robust relay tracking of the same target.