The utility model provides a belt pulley with a belt breakage protection device. The belt pulley comprises a first belt pulley body, a second belt pulley body, a center shaft, an ejection device and a bearing. The second belt pulley body and the first belt pulley body are arranged side by side in the axial direction. The center shaft is sleeved with a first axle and penetrates through a second rim. The ejection device comprises an elastic element set, an elastic element shell, first supporting arms and second supporting arms. The center shaft is sleeved with the elastic element set which stretches and retracts in the radial direction of the center shaft. The elastic element set is coated with the elastic element shell. One end of each first supporting arm is connected with the outer wall of the elastic element shell and the other end of each first supporting arm penetrates through a first rim. One end of each second supporting arm is connected with the outer wall of the elastic element shell. The bearing is arranged between the second rim and the elastic element shell in a sleeved mode, the second supporting arms penetrate through the inner ring and a holder, and multiple clamping grooves for locating the second supporting arms are formed in the inner wall of the outer ring. The second belt pulley body is a standby belt pulley body and can run continuously after a belt of the first belt pulley body is broken.