The invention discloses a water level monitoring method. The method comprises the following steps of: performing early detection on an analog signal video which is generated at a water level scene photographed by a video camera to keep the analog signal video in a standard photometric range; performing target detection on the analog signal video which is subjected to the early detection to separate a background and a target from the analog signal video, wherein the background in the analog signal video comprises a warning line, and the target is a buoy which floats at the water level scene; tracking the separated target to acquire a track of the target; judging whether a water level is normal by detecting whether the track of the target exceeds the warning line; and giving an alarm when the water level is abnormal. By the method, the alarm can be timely given when the water level is abnormal.