The invention discloses a power distribution device based on a differential mechanism for two reamer heads of a cutter suction dredger. The power distribution device comprises a main shaft which is connected with an engine. The main shaft is also connected with the differential mechanism. A transmission shaft of the differential mechanism is connected with two half shafts. Each half shaft is connected with a hydraulic oil pump. The hydraulic oil pumps are connected with hydraulic motors of the reamer heads through oil delivery pipes. The hydraulic motors drive the reamer heads to work. Electronic brakes are arranged on the two half shafts respectively. Hydraulic sensors and flow sensors are arranged in the oil delivery pipes. Collected data are transmitted to an electric control center through the hydraulic sensors and the flow sensors. The electric control center controls the electronic brakes on the two half shafts according to the data, so that the rotating speeds of the two reamer heads are controlled. The invention further provides a power distribution method based on the differential mechanism for the two reamer heads of the cutter suction dredger. By the adoption of the device and method, the rotating speeds of the reamer heads on the two sides can be coordinated automatically, and the cutter suction efficiency of the cutter suction dredger is improved.