Pump coupler is the key passive optical component for the high power fiber laser. Multiple pump lights are efficiently coupled into the double- clad fiber, the required pump power can be provided for the realization of high power fiber laser. Pump coupler is the first problem to be solved for the research of the high power fiber laser. A high power side- pump coupler is developed with the method of hydrogen- oxygen flame fusion, when the maximum pump power is 100 W, the coupling efficiency is 94% , the signal insertion loss is 0.15 dB, the additional loss is 0.2 dB, the splitting ratio of main fiber is 99%, and the directionality is 22.5 dB. A hundred-watts fiber laser with an output power of 103 W at 1080 nm is built when the maximum pump power is 185 W. Optical- optical conversion efficiency is 56% . The high power side-pump coupler can be used as the pump coupler of the hundred-watts, and even kilowatt high power fiber lasers.