Abstract: Compressive arch action (CAA) in reinforced concrete beams develops from the coupled compressive-flexural behavior under statically indeterminate conditions. With the introduction of prestressing tendons, the dynamic redistribution of internal forces within both the structural members and the prestressing system renders the compressive-flexural mechanism considerably more complex, making its direct experimental measurement challenging. This study established a refined numerical model of unbonded prestressed concrete (UPC) continuous beams using the finite element analysis software LS-DYNA. The accuracy of the model was validated via existing experimental tests. Based on this model, the collapse resistance contributions of different mechanical mechanisms during CAA stage were investigated using a proposed analytical calculation method of collapse resistance. Research findings indicate that straight tendons can provide resistance throughout the entire collapse progression process. However, excessive prestress may lead to premature cracking and spalling of the concrete, reducing structural ductility and thereby suppressing the development of CAA. This research provides a reference for numerical modeling and collapse mechanism analysis in studying the progressive collapse resistance of UPC frame structures.