The invention belongs to the measurement technology field and particularly relates to a seabed pipeline bending deformation state monitoring system and a method. A data processor and a multi-beam sonar controller are arranged in a cabin of a measurement ship, the multi-beam sonar controller is connected with a multi-beam sonar emission energy transducer and a sound signal reception energy transducer through cables, the multi-beam sonar emission energy transducer and the sound signal reception energy transducer are fixed on a ship side at one side of the measurement ship through a multi-beam system fixing mounting auxiliary device and are arranged below the sea surface, the data processor is connected with the multi-beam sonar emission energy transducer, the sound signal reception energy transducer, multi-beam system GPS positioning equipment, a measurement ship attitude sensor, a sea level rectification sensor and a water depth measurement device through cables, and stinger GPS positioning equipment is connected with the data processor in a wireless mode. The seabed pipeline bending deformation state monitoring system timely monitors a deformation state of a pipeline laying process, acquires pipeline stress strain parameters through analysis and provides operation reference for pipeline construction.