Abstract: Sandstone is the most common rock type of grottoes in China. It is loose, porous, and prone to strong water rock dissolutions, which seriously threatens the stability of the rock mass of grotto temples and valuable artistic values. In this paper, the damage law under the condition of water rock dissolution of the sandstone in the AnYue Grottoes is studied in both macro-mechanical and micro-structural aspects through laboratory dry-wet cycle simulation tests, and the phase heterogeneity deterioration characteristics and damage mechanism of grottoes sandstone are discussed. It is found that the basic physical property indices of rock such as quality, wave velocity and strength all gradually deteriorate with the proceeding of dry-wet cycles. The changes of pores, micro morphologies and mineral contents are characterized by phase degradations, which are the three key factors determining the phase heterogeneity degradation effect of sandstones. The degradation damage can be divided into three phases: the first phase dominated by pore expansion, the second phase dominated by micro contact relationship damage and the third phase dominated by transgranular fracture. Based on the phase heterogeneity deterioration characteristics and damage law of sandstone under dry-wet cycles, this paper further proposes a deterioration damage evolution model of sandstones, and gives targeted suggestions for the repair of grottoes rock mass, which to some extent provides a theoretical basis for the protection of grottoes rock mass affected by long-time water rock dissolutions.