A novel high-power semiconductor laser diode (LD) with very large cavity using multi-active -layer cascaded by tunnel-junction was developed. The window size of the LD was enlarged extremely and less than 20 degree of the lasing beam divergency was obtained，which benefits the coupling between the LD and the optical fiber. Many types of lensed fibers were used to test with the LD and the coupling efficiencies were increased over 30% compared with the conventional LD.