As a common phenomenon after artificial reefs are put into operation, reef settlement will have an impact on the flow field around artificial reefs.In order to study the change of flow field effect under different settlement of porous square artificial reef, the flow field around single reef to five different settlement degrees was simulated by using computational fluid dynamics (CFD) technology and Fluent software when the fixed incoming flow velocity was 0.8 m/s.The results showed that compared with the case without settlement (initial state), when the settlement degree was 20%, the maximum height of upwelling decreased by about 1m, the maximum upwelling velocity increased by about 0.015 m/s, the lateral velocity increase area (greater than the incoming velocity) expands to about 1.5 times, at the same time, the permeable area of the reef back flow surface increased, and the back vortex area moved about 2 m along the flow direction. The flow field around the reef becomes more complex to some extent;When the settlement degree is 40%, the maximum value of upwelling velocity decreases by about 0.01 m/s compared with the initial state, and the increasing area of lateral flow is basically the same. At this time, the permeable area of reef back flow surface changes greatly, and there is a trend of counterclockwise vortex; When the settlement reaches 60%, the flow field effect around the reef begins to decrease significantly, the maximum height of the upwelling decreases by about 3.2 m compared with the initial state, the maximum velocity of the upwelling decreases by about 0.6 m/s, the distance between the lateral velocity increasing area and the wall shortens by about 0.4 m, and the back vortex area seemed disappear;When the settlement reaches 80%, the flow field effect of reef body basically lost.The results showed that for the porous square artificial reef, the artificial reef can still play a good flow field effect when the settlement degree is less than 40%; When the settlement of the reef reaches 60%, the complexity of the flow field around the reef is obviously lost compared with the initial state. Then, with the increase of the settlement depth, the flow field effect of the reef gradually disappears.