In order to study the two-dimensional(2D)flow in the Yazidang Reservoir, terrain pretreatment was carried out using the image processing method and Google Earth(GE)software. The initial terrain of the reservoir was obtained through image mosaicking, mathematical morphology, and measured data. A 2D RNG k-ε turbulence model was established, reasonable boundary conditions and initial conditions of the flow module of the established model were set, the equations were discretized using the finite volume method, and a mesh was divided using the advancing-front method. The flow field in the reservoir and the depth-averaged velocity at sections near the water inlet and the water power were simulated. The results show that accurate and detailed reservoir terrain can be obtained using the image processing method and the GE software. The numerical simulation results of the flow field and the depth-averaged velocity at critical positions show that the simulated and measured values are in strong agreement.