Due to the constraints of land resources and environment and the continuous progress of science and technology, human beings have entered an era of deep exploitation of marine resources and utilization of marine space. With the depletion of offshore fishery resources and the aggravation of marine pollution, the construction of marine ranching has become an important measure to improve marine ecological environment and repair fishery resources. Among them, artificial reefs are the infrastructure of modern marine ranching, and ensuring the normal utility of artificial reefs is the key link of marine ranching construction. In order to study the influence of the upstream inflow angle on artificial reefs at different velocities, in this paper, based on Ansys-Fluent, the RNG k-ε turbulence model is used to conduct numerical flume simulation. The hydrodynamic characteristics of a 3 m cube-diagonal open-hole fish reef under three incoming velocities (0.5, 1.0 and 1.5 m/s) and four attack of angles (0°, 15°, 30° and 45°) were compared and analyzed, including upwelling volume, back eddy volume, resistance and overturning moment. Studies have shown that there are upwelling and back eddy areas with significant characteristics in and around the artificial reef. The scale of the flow field is basically not affected by the flow velocity, while flow velocity is the main factor affecting the stability of cube-diagonal hole-opening reef. The greater the flow velocity, the greater the resistance and overturning moment acting on the reef, and the worse the stability of the reef. The flow field effect of artificial reefs is mainly influenced by the inflow angle. The flow field effect scale of the artificial reefs reaches the optimum when the inflow angle is 30°-45°, and the upwelling volume and back eddy volume reach the maximum when the reef is 45°. The weight assignment method is used to introduce a comprehensive evaluation model for the construction effect of artificial reefs. Through comprehensive evaluation and analysis, the sea area with the maximum flow velocity not exceeding 1 m/s should be selected when placing artificial reefs without considering the conditions of seabed sedimentation, wind and waves, etc. Moreover, the construction effect of the reef is the best when the inflow angle is within the range of 30° to 45°, which can provide a certain theoretical basis for the artificial reef deployments in practical engineering.