A well cover assembly includes a monitoring device and a well cover. The well cover includes a first protrusion and a second protrusion. A through hole is defined on the well cover and surrounded by the second protrusion. The monitoring device can be installed on the well cover. The monitoring device includes a monitoring terminal and a fixing bracket. The fixing bracket includes a first bracket and a second bracket. One end of the first bracket is fixed to the monitoring terminal, and another end can protrude from the through hole. The second bracket is connected to the end of the first bracket protruding from the through hole, the second bracket can extend from the end of the first bracket toward an edge of the second protrusion and toward the first protrusion. The second bracket further can clamp with each of the second protrusion and the first protrusion.