Artificial reef is an important part of marine ranching, which is of great value for the restoration of marine ecological environment and the improvement of fish catch. Placement of artificial reef can make the flow field around change, which has an important impact on fish feeding and sheltering. This paper studies hydrodynamic characteristics of artificial reef, and analyzes the flow field of combined pyramidal artificial reef with Fluent and based on N-S equation. By comparing the flow field changes under 4 different flow rates (0.1, 0.2, 0.3 and 0.4 m/s), the distribution characteristics of vortices and pressure around are obtained. Three-dimensional turbulent zone of such artificial reef is provided and compared with other types of artificial reef. The results show that the vortex is mainly distributed in the rear area of the diversion tray, and the farther, the weaker; at different flow rates, the maximum height of the ascending flow is about 1.53 times of the height of the reef, the height of the reef vortex area is about the height of the artificial reef, and the length of the vortex zone increases with the velocity of the water; at different flow rates, the range and size of the turbulent zone remain the same..