A probe monitoring system for riverbed elevation monitoring at bridge piers is revealed. The system includes a housing, a measuring rod, a moving member, a control module, a photographic unit and a sensing unit. The housing is fixed on the pier. Both the moving member for driving the measuring rod and the control module for control of the moving member are mounted in the housing. When the control module drives the measuring rod to move downward and the sensing unit on the bottom of the measuring rod approaches the riverbed, a sensing signal is sent to the control module. Thus the moving member stops moving the measuring rod and the photographic unit takes pictures of the measuring rod to generate an image. Then the riverbed elevation is obtained according to the image or the movement of the moving member and is sent to a remote monitor unit for real-time monitoring.