Rapid water-loss is one of the important characters on thin layer mortar.The testing methods, such as the velocity of water migration, the strength of interfacial bonding, XRD, SEM, FTIR and TD-DSC-DTG were used to research the interface and microstructure of thin layer mortar with continuous moisture migration from the thin layer mortar to aerated concrete.The results show that the rate and the amount of water migration on the interface from mortar to substrate dropped significantly with the increase of viscosity of mortar.There was also a good corresponding relation on the tensile bond strength of the interface and mortar viscosity, which means that the interface bonding strength increased with the increase of the viscosity of mortar.The XRD analysis results of the interface of hydration products show that the characteristic diffraction peaks of Ca(OH)2 were obviously appeared at the interface, which means hydration products are densely distributed at the interface.The phenomenon indicates that the interfacial properties were improved because the migration of moisture from mortar to interface.These discoveries have revealed the important implications to inprove the interfacial properties of adhesive mortar or plastering mortar through controlling mortar viscosity.