A monitor system for monitoring riverbed elevation changes at bridge piers is revealed. The monitor system includes a container, a rail, a holder, a photographic unit, a processor and a transmission unit. The container is disposed at a pier under the water and the rail is mounted in the container. The holder is arranged at the rail and is moved on the rail. The photographic unit is disposed on the holder to capture a monitor image of a riverbed under the water. As to the processor, it processes the monitor image so as to learn elevation change of the riverbed under the water. By the transmission unit, the riverbed elevation change is sent to a remote monitor unit so as to get the riverbed elevation according to the riverbed elevation change. Thus the riverbed elevation change at the bridge pier is monitored in real time.