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• Water desalination laws and related mechanisms of HCM were investigated by the MD simulations. • Microscopic mechanism of raw water temperature affects HCM membrane flux was clarified. • Diffusion form of free-state water molecules in the membrane micropores of HCM was ascertained. With LAMMPS software, the non-equilibrium molecular dynamics (NEMD) simulations study was conducted for the membrane distillation process with the hydrophobic α-Al 2 O 3 ceramic membrane (HCM). It could further help to explain the macroscopic laws and phenomena that appeared in the membrane distillation tests with HCM. In this study, the average temperature (T r) of raw water and the negative pressure (P con) on the cold side of HCM were taken as the investigation variables to research the microscopic water desalination performance of HCM, transport/diffusion properties of water molecules, and related mechanisms. The results showed that the root means square displacement (MSD) of water molecules on the cold side of HCM positively changed with time by the linear trend. The height of the transmembrane energy barrier mainly depends on the atomic structure of the HCM. The diffusion type of free-state water molecules in the membrane micropores of HCM was the main ballistic-transport-like accompanied by rebound-jump. The influence level of T r on the number of water molecules in the cold side of HCM was much greater than that of P con under the dynamic equilibrium state. The essential reason T r determined the HCM molecular flux was that it changed the hydrogen bond lifetime in the microporous membrane of HCM. [ABSTRACT FROM AUTHOR]