In this paper, we investigate a (2 + 1)×1 side pump combiner with high power handling capability and high beam quality numerically and experimentally. Through theoretical research, we have found how the combiner’s parameters influence its pump coupling efficiency and maximum load power. According to the numerical analysis, we fabricate a side pump combiner, which consists of two pump fibers (220/242 µm, NA = 0.22) and a signal fiber (20/400 µm, NA = 0.06/0.46). The coupling efficiency of the side pump combiner is 97%, which is tested under 2 kW input pump power. Using two side pump combiners and four high power 976 nm laser diodes, a bi-directionally pumped fiber laser oscillator is constructed and tested. The fiber laser oscillator’s maximum output power is 2150 W when injecting 3070 W pump power, corresponding to a slope efficiency of ∼72%. No stimulated Raman scattering or transverse mode instability was observed during the operation test. Thanks to the advantage of maintaining high beam quality of the home-made side pump combiner, this all-fiber laser oscillator achieves single mode laser output (M2=1.05) even when the output power increases to more than 2 kW. By further improving the fabrication technique and using larger core fibers, output laser power could be greatly increased, which is very important for high-power fiber lasers.