Abstract: Double-clad doped optical fiber is used in high-power fiber lasers and fiber amplifiers. Compared to the large divergence angle of the multimode pump beam emitted by the semiconductor pump laser, its inner cladding diameter is small, which makes effectively coupling pump beam to the inner cladding of the double-clad doped optical fiber difficult. A kind of fused side-pumped coupler is developed, which enhances the pump power and realizes multi-point pump to the gain fiber. It is used in the double-clad fiber amplifier. It has good security and stability, a coupling efficiency of 70%, a ratio of 98% coupled signal light, and over 50dB isolation of the signal input and pump beam input, and 27dB isolation of the pump beam to the counter -propagation beam are achieved. The fused biconical taper side-pumped coupler has compact structure, good coupling efficiency and system stability, which meets the requirements of the high power fiber lasers and fiber amplifiers.