In order to study the mechanical properties of coral aggregate seawater concrete (CASC) subjected to the penetration of scaled earth penetrator, firstly, the penetration depth and damage of CASC and ordinary sand-gravel concrete under the same conditions were compared by experimental research, and the influence of concrete strength and projectile velocity on penetration performance was analyzed. Then, the three-dimensional mesoscopic model is used to simulate the test conditions, and the failure process and failure mechanism are analyzed. The results show that under the same penetration conditions, as the strength of CASC increases, the crater diameter becomes larger, which is consistent with the conclusion of ordinary concrete (OPC). During the penetration process, the CASC and the mortar are destroyed as a whole. At the same time, as the penetration speed of the projectile increases, the width of the crack on the surface of the target increases. When the projectile velocity is low, the anti-penetration performance of CASC with the same strength is not as good as that of OPC with the same strength. For the target with a thickness of 25 cm, the penetration depth of the concrete target with the same strength will increase with the increase of the velocity of the projectile. When the velocity of the projectile is constant, the penetration depth of CASC will decrease with the increase of the strength. The numerical simulation results obtained by using the K & C mesoscopic model are in good agreement with the experimental results, indicating that the model and its model parameters have high reliability in the analysis of CASC penetration mechanical properties.