In order to study the effect of the size of coral coarse aggregate on the mechanical properties of coral concrete, this paper carried out continuous grading of coral concrete with 5-10, 5-20 mm and 5-31.5 mm under three water-cement ratio conditions of 0.50, 0.40 and 0.33. The research results show that the fluidity of newly mixed coral concrete is significantly affected by the aggregate particle size, and the larger the aggregate particle size is, the worse the fluidity will be. The main reason is that its bite-and-lock action is not conducive to the flipping of the aggregate, which reduces the liquidity of the fresh coral concrete. Moreover, particle size has a certain influence on the destruction process of coral concrete, which is mainly reflected in the amount of aggregate penetrating the failure at the failure surface, but the difference in the final failure form is not obvious. Large-size coral aggregate is conducive to enhancing the resistance strength of coral concrete under the condition of low water cement ratio.The irregular arrangement of coral -debris strip characteristic particles shows a certain bridging ability when the strength of cement mortar is low, and the enhancement effect gradually decreases with the increase of the cement motar strength.