DT-LFJ-XXX vibrating string displacement meter is a string sensor whose internal steel string resonant frequency changes with the displacement length. The frequency can be measured by a vibrating string collector and converted into displacement. It can be used to measure the opening and closing degree of expansion joints and cracks of structures, and can be used to monitor the displacement and cracks of large structures such as DAMS, earth DAMS, Bridges, roads, tunnels, tall buildings and civil air defense projects.