Based on the analysis of propagation ray theory in cladding layer of multimode power delivery optical fiber and the high-power diode laser pigtail fiber bending experiment, part of the light transports into the cladding layer because fiber bending is found transporting back to the fiber core, especially when the length of the bending fiber is short. It means that transmission efficiency of bending fiber is determined by bending radius and bending length. A high transmission efficiency of power in fiber at small bending radius can be obtained when the length of bending is well chosen.