In order to investigate the effects of slot position on the hydraulic characteristics of a vertical slot fishway pool, the RNG k-ε turbulence model and velocity-pressure coupling SIMPLE algorithm were used to numerically simulate the fishway under different working conditions. The results indicate that the slot position rarely influence the pattern of mainstream flow, the attenuation of velocity along main stream, and the velocity distribution at the vertical slot section. The slot position affects the distribution, area, and flow field of the recirculation zone by changing the location of the mainstream zone. When the distance between the vertical slot and the sidewall is 25% to 35% of the pool width, the flow pattern in the fishway is reasonable and the efficiency of fish passing is significantly improved.