Polymer viscosity is severely degraded in high-temperature, high-salinity (HTHS) reservoir environments and under shear conditions. However, the impact of polymer viscosity on oil recovery after shear through perforations or over long distances remains unclear. This study investigates the performance variations and governing mechanisms of three polymers—ultra-high molecular weight partially hydrolyzed polyacrylamide (HPAM), a temperature- and salinity-resistant ultra-high molecular weight polymer (NKSP), and an ultra-high temperature-resistant low-hydrolysis polymer (PSVP)—under HTHS conditions and perforation/long-distance shear. The results indicate that the shear resistance follows the order: PSVP > NKSP > HPAM. Perforation shear significantly reduces the molecular weight and viscosity of HPAM and NKSP, whereas long-distance shear has a minor effect on the viscosity loss rate and molecular weight of the three polymers. The ability to establish high flow resistance follows the order: NKSP > PSVP > HPAM, with corresponding enhanced oil recovery (EOR) values of 12.44%, 11.18%, and 7.89%, respectively. Further evaluation of the effects of different ions on NKSP reveals that, under anaerobic conditions at 10 mg/L, both the EOR and viscosity retention rate follow the trend: S²?/Fe²? > S²? > Fe²?. Conversely, higher Ca²? concentrations lead to lower EOR and viscosity retention rates, exhibiting a nonlinear relationship with polymer viscosity. At elevated temperatures, long-distance shear exerts a significant and continuous impact on the polymer''s viscosity loss rate and EOR. Appropriately increasing the polymer concentration helps maintain the viscosity retention rate after shear, and a nonlinear relationship is observed between post-shear viscosity and EOR. This study clarifies the key control mechanisms of long-distance polymer shear in HTHS reservoirs, providing a theoretical basis for optimizing injection allocation in field applications.