Tantalum-tungsten alloys present a significant challenge in machining due to the severe tool wear. Cemented carbide tool materials have a significant impact on the machinability of tantalum-tungsten alloys. In this study, the influence of binder phase Co content on the dry sliding behavior between tungsten carbides and Ta-2.5   W alloys was investigated. Two WC/Co carbides with different Co contents—6   wt.% (UF6) and 10   wt.% (UF10)—were chosen as the research subjects. Pin-on-disc dry sliding experiments were conducted with sliding velocities ranging from 90 to 180   m/min. The coefficient of friction, wear rate, and evolution of surface morphology were analyzed under different velocities, and the thermal-mechanical distribution characteristics at the interface between the cemented carbide and the tantalum-tungsten alloy were simulated. The results indicated that the coefficient of friction of UF6 was higher than that of UF10 at all velocities. The wear rates of both materials reached their minimum values at 120   m/min and then increased significantly at velocities of 150–180   m/min. The primary wear mechanism was adhesive wear. At velocities of 90–120   m/min, UF10 exhibited superior wear resistance due to its higher Co content. At higher velocities of 150–180   m/min, due to friction-induced thermal softening of carbides, UF6 with low Co content exhibited a lower wear rate because of its higher retention of strength. The research results provided experimental evidence for selecting and optimizing cutting tool material for Ta-2.5   W alloys.