Mode instability has become the major limitation for power scaling of fiber lasers with nearly diffraction-limited beam quality. Based on mode coupling theory, we establish a semi-analytical model to simulate mode instability effect. Compared with co-pumped fiber laser, counter-pumped and bi-pumped fiber lasers reveal mode instability threshold enhancement in our theoretical model. Compared with that of the co-pumped scheme, the experimental mode instability threshold of the counter-pumped fiber laser is enhanced by at least 50%. Moreover, we demonstrate a 2 kW high power narrow-linewidth counter-pumped fiber laser with high beam quality.