Low temperatures induce novel effects and phenomena. Tribological studies of MoS 2-Ti-LaF 3 films in a low temperature vacuum environment revealed that trace water molecular condensation at a specific temperature promotes a unique MoS 2 tribochemical reaction, resulting in high friction and wear. The MoS 2-Ti-LaF 3 films were characterized using Raman spectroscopy, XPS, FESEM, TEM, and in situ vacuum quadrupole mass spectrometer. The results indicate that at 150 K, water molecules condense and physically adsorb on the film's surface, inhibiting MoS 2 shearing and rearrangement during friction. Under heavy load and friction heat, the adsorbed water molecules and trace O 2 further promote the chemical reaction with many damaged MoS 2 edge suspension bonds, defects, and other active sites, forming non-lubricious MoO 3. MoO 3 is transferred to the steel ball's surface, resulting in increased friction and wear, and its oxidation degree is positively correlated with the friction coefficient. This new discovery provides a reference for the research of low temperature solid lubrication materials and broadens the consideration and selection of actual working conditions.