A three-dimensional finite element numerical model was established to simulate the gravity anchor bottoming out and penetrating into the lakebed, considering different soil conditions. Gravity anchors with different geometric sizes were examined. The penetration process and the flow of soil around the anchor body were analyzed using the fluid-solid coupling and particle tracking finite element technology. The results show that solid cylindrical gravity anchors should be selected with caution, as that in natural lakebed conditions, the full anchor body could penetrate into the lakebed and be buried by soil. If the lakebed soil condition is sand type, the gravity anchor penetration depth will be significantly smaller than that under natural conditions, which coins could be one of the measures to reduce the lifting capacity requirement during anchor recovery. The analysis results presented in this paper can provide reference for the selection, design and use of the anchor body of the test platform in the lake.