Abstract: Application of coral waste in concrete is an effective strategy to produce building materials suitable for offshore island construction, but excessive application of coral waste can lead to drastic degradation of concrete properties. In order to improve the replacement ratio of coral waste while ensuring the performance of mortar, this study combined coral sand (CS) and coral powder (CP) to replace part of the aggregate and binder to produce mortar, and the effect of CS substitution ratio on the mechanical properties, autogenous shrinkage and drying shrinkage of mortar was investigated, and its influencing mechanism was analyzed in combination with microstructure and pore structure. The results demonstrate that the mortar produced by combined application of 10wt%-40wt%CS and 10wt%CP has higher strength than the mortar without CS. When the replacement ratio of CS is 30wt%, the strength of the mortar is the highest, and its 28 days compressive strength is increased by 29.50% compared with the reference group. Meanwhile, with the increase of CS content, the autogenous shrinkage of mortar decreases. When the CS content is 40wt%, the 28 days autogenous shrinkage value of the mortar is decreased by 33.74%, compared with the reference group. In addition, the addition of CS is also beneficial to reduce the drying shrinkage of mortar, and the drying shrinkage of mortar reaches the lowest when the substitution ratio of CS is 30wt%. The porous structure of CS makes it tightly occluded with the cement matrix, and its internal curing effect also promotes the improvement of interface performance. The results of the specific surface area (BET) also show that adding 30wt%CS reduces the porosity of the sample, but further increasing the CS content is not conducive to the development of the pore structure of the sample.