<p>This study combines finite element (FE) and molecular dynamics (MD) simulations to establish a multiscale analysis framework, systematically investigating the effects of drill pipe rotary speed and lateral contact force on casing wear behavior and the underlying physical mechanisms. The FE results indicate that rotary speed and lateral contact force exacerbate casing wear through distinct mechanisms. A “pressure drop” effect, resulting from the expansion of the contact area during the wear process, is observed, which explains the transition of wear depth evolution from nonlinear to quasi-linear over time. MD simulations further elucidate the distinct mechanisms by which the two factors aggravate wear: Increasing rotary speed primarily intensifies atomic collisions and frictional heat, promoting material thermal softening and surface layer exfoliation; whereas increasing lateral contact force elevates interfacial contact stress and exacerbates stress concentration, leading to deeper crystalline structure damage and plastic plowing. This work contributes to the mechanistic understanding of casing wear and provides a basis for numerical prediction of casing wear.</p>