Abstract: Clay minerals can experience strong tensile and compressive forces in extreme environments such as the deep sea and subsurface. Moreover, the presence of water films greatly affects the mechanical properties of clay. To explore these properties, we use a molecular dynamics (MD) simulation method to study axial mechanical behavior and failure mechanisms of hydrated kaolinite. Two types of deformation are applied to kaolinite examples with varying water film thicknesses: stretching along the transverse (x) direction, and compression along the longitudinal (z) direction. The ultimate strength of kaolinite with different water film thicknesses ranges from 8.12% to 27.53% (for stretching along the x-direction) and 15.71% to 26.02% (for compression along the z-direction) less than that of dehydrated kaolinite. Additionally, we find that hydrated kaolinite is more prone to tensile than compressive failure under high stress. When stretched along the x-direction, the diffusion of water molecules results in unstable tensile properties. When compressed along the z-direction, water films weaken the compressive strength of the system and lead to greater compressive deformation, but also delay the time at which the system fails. Furthermore, we investigated the failure mechanisms of hydrated kaolinite through analysis of interaction energies. The tensile failure along the x-direction is caused by the breaking of the covalent bonds in the clay mineral sheet. On the other hand, the compressive failure along the z-direction is due to the crushing of the internal structure of the clay mineral sheet.