Mural plaster deterioration poses great threat to the long-term preservation and daily maintenance. The migration of soluble salts by moisture movement is one of the most important factors that causes mural plaster deterioration. The plaster plays an important role in supporting the murals. The soil-water characteristic of the mural plaster is related to the formation and development of mural deterioration. In order to study the soil-water characteristic curve (SWCC) of mural plaster in full suction range, laboratory reconstituted plasters were prepared by the same materials as the mural plaster in Mogao Grottoes, and the pressure plate test method and vapor equilibrium technique were employed. The SWCC test data was fitted by van Genuchten (VG) model and Fredlund Xing (FX) model. The SWCC of the reconstituted plaster samples with different compositions showed different characteristics, while the morphological differences between the coarse plaster and the fine plaster on the SWCC were not obvious. Under the same suction condition, the moisture content of the coarse plaster is higher than that of the fine plaster, and the coarse plaster has the characteristics of rapid release of moisture in the high suction range. By analyzing the trend of the SWCC in the high suction range, it is recommended that the humidity in the Mogao Grottoes should not exceed 58% in daily maintenance, and the humidity should be stable with no major fluctuations. Based on the experimental data in the full suction range, highly accurate SWCC can be obtained.