The invention discloses a cutter-suction device based on ultrasonic-assisted rock breaking, and a rock breaking method. The device comprises a cutter-suction dredger cutter-suction device, a connecting device and an ultrasonic-assisted device. The cutter-suction dredger cutter-suction device comprises a bridge frame, a tail shaft, an underwater pump, a suction pipe, a bridge frame pulley, a transverse movement pulley, an underwater motor, a reamer and a reamer shaft. The connecting device comprises an upper cover, a plunger cylinder and a support. The ultrasonic-assisted device comprises an ultrasonic generator, an ultrasonic switch and an ultrasonic device. According to the cutter-suction device based on ultrasonic-assisted rock breaking, and the rock breaking method provided by the invention, through the ultrasonic-assisted device, an ultrasonic cutter bit and a rock achieve resonance, so that the rock forms cracks and fissures, the completeness of the rock is broken, the strength ofthe rock is reduced, and the digging resistance of the reamer is correspondingly reduced; and in addition, from officinal cutting on, the reamer and the ultrasonic device start to work at the same time, so that the excavation ability and the efficiency are improved, the dredging energy consumption is reduced, and the aim on optimizing the cutter-suction dredger cutter-suction device and an application method thereof is finally achieved.