Abstract: In order to explore the direct shear mechanical properties and constitutive relationship of coral seawater sea-sand concrete (CSSC) after high temperature, the direct shear test of CSSC after high temperature was designed and completed with maximum high temperature T and constant temperature duration H as changing parameters. The failure mode and stress-displacement curve of CSSC under direct shear were observed, and the effects of T and H on the shear strength, volume expansion and mass loss of CSSC were obtained. Then the damage evolution process of CSSC after high temperature was analyzed and compared. The results show that the high temperature leads to non-uniform temperature fields, surface cracks and corner cracks in CSSC. With the increase of T and H, the shear strength of CSSC decreases gradually while the volume expansion rate and the mass loss rate gradually increase. When T > 400℃, the decrease rate of shear strength accelerates. When T = 800℃, the direct shear strength of CSSC is only 39% of that at room temperature. Finally, the direct shear strength calculation equation of CSSC after high temperature and its damage constitutive model are proposed.