The invention discloses a displacement-sensor-based angle monitoring system, which comprises a data processing unit, an execution unit and a signal acquisition unit, wherein the signal acquisition unit comprises a fan-shaped angle conversion mechanism, a stay wire displacement sensor to be fixed with a river bank and a poking mechanism; the fan-shaped angle conversion mechanism comprises an installation support fixed on the river bank, a fan-shaped plate and a catch lever; the fan-shaped plate is matched and connected with the installation support by a pin shaft, and the arc surface of the fan-shaped plate is provided with an arc-shaped groove; the catch lever is fixedly connected with one end, which is close to the closing direction of a floating body door, of the fan-shaped plate; the stay wire displacement sensor is in communication connection with the data processing unit and is provided with a stay wire and a wire outlet hole, and the stay wire is fixedly connected with one end, which is close to the closing direction of the floating body door, of the fan-shaped plate; the poking mechanism comprises a fixed plate to be fixed on the upper part of the floating body door, a poking lever base and a poking lever; the poking lever is embedded into the poking lever base and is matched and connected with the poking lever base; and the poking lever can poke the catch lever when rotating with the floating door by the relative position relation of the poking lever and the catch lever.