A high power all-fiber (2+1)×1 side-pumped combiner based on tapered-fused method is developed. The theoretical model of the combiner is set up through simulation software, and the coupling efficiency of combiner is calculated. A side-pumped combiner is fabricated. The coupling efficiencies are 98.2% and 96.3% for two pump arms respectively at the pump power of 600 W, and the insertion loss of signal light is about 0.11 dB. The combiner is applied to construct a kilowatt-class fiber laser amplifier. The output power is 1.426 kW at 1080 nm, when the power of bidirectional pumping light reaches 1.8 kW.