Abstract: Efflorescent and detachment destroy of the wall-paintings of the Mogao Grottoes in Dunhuang are due to water-salt transfer.This is the first time to test moisture content by drying,take samples at a exploratory well of 20 meters below the Mogao Grottoes cliff top.The test results show that the average moisture content of the conglomerate is 1.6% and the distribution is relatively equable.There are silty clay and fine-sand layers in the cliff rocks.The moisture content is 24% in the silty layer and 3.6% in finesand layer.The presentation of moisture distribution provides a basis for studying the wall paintings pathologies and conservation of the Mogao Grottoes.