Combining an amorphous carbon (a-C) film with a lubricating oil can significantly improve the friction performance and lifetime of moving mechanical components. However, the friction mechanism is not well understood owing to a lack of information regarding the structure of the interface when exposed to high contact pressure. Here, we select linear alpha olefin, C₅H₁₀, as a lubricant and study the evolution of the structure of the a-C/C₅H₁₀/a-C sliding interface under contact pressure via reactive molecular dynamics simulation. Our results suggest that introducing C₅H₁₀ into the a-C/a-C interface reduces the friction coefficient by up to 93% compared with no lubricant, although the lubricating efficiency strongly depends on the contact pressure. In particular, increasing the contact pressure not only induces the binding of the lubricant with a-C, but also facilitates the dissociation of the C₅H₁₀ carbon-carbon skeleton by specific scissions, which governs the friction behavior. These results disclose the underlying lubrication mechanism and could enable the development of new and effective lubricating systems with long lifetimes.