Casing wear is an increasingly typical problem that leads to a decrease in collapse resistance in deep wells, ultradeep wells, horizontal wells, and extended reach wells. Casing wear can be harmful during drilling and can undermine wellbore integrity during production. It is essential to consider the collapse resistence of worn casing during casing design. In this article worn casing is described as geometric imperfections in the ovality of the inner wall and nonuniformity of wall thickness, and a new empirical formula is established to compute the collapse resistance of crescent-worn casing under nonuniform loading. Collapse testing has validated the formula. Calculated results are very close to experimental results, satisfying engineering requirements quite well. The new empirical formula can provide a theoretical basis for casing design in complicated formations.