Owing to the increase of dam construction, fish migration and fish spawning have been severely affected. In order to maintain the fish to survive and multiply, many fishways have been built. In this paper, a series of numerical model tests were conducted to simulate the flow fields of vertical-slot fishways via the fluent software. And afterwards physical model experiments were performed to verify the numerical simulation. The impacts of guide plate length and lead angle on the flow field were analyzed. The results show that when the discharge and the length to breadth ratio of the fish-pond are constant, ignoring the influence of the side wall, the larger the lead angle is, the faster the vertical slot jet will decay, the more meandering the mainstream will be, and the easier the mainstream will collide the side wall. The results also show that the length of the guide has barely any direct effect on the spread and decay of mainstream, but it will impact on flow field through walls as it changes the location of mainstream in the fishway.