There are many factors affecting the wear behavior of the dynamic seals tribo-pairs in pneumatic downhole tools, such as tribo-materials, load, and surface roughness. In this work, to investigate the influence of surface roughness of stator on the dry sliding behavior against rotor in pneumatic downhole motor, under a load of 45 N optimized by our previous work, a tribo-pair consisted of a Qbe2 beryllium bronze pin with constant roughness (0.1 μm) and a 38CrMoAlA steel plate with different roughness (0.1-0.8 μm) was designed for pin-on-plate dry sliding tests to simulate the friction and wear behavior of the copper-steel soft–hard tribo-pair dynamic seals. It was revealed that the initial values of instantaneous friction coefficients were almost equal for all the tribo-pairs, the change trends of friction coefficients were basically similar, the material removal mainly occurred on the copper pin, and the dominant wear mechanism was adhesive wear. With the increase in the surface roughness of the steel plate, the adhesive wear of the matching materials was reduced, while the plowing effect of the asperities on the copper pin was enhanced, and the oxide formed on the friction surface plays a certain role in reducing friction by lubrication. When the surface roughness of the steel plate is 0.2, the tribo-pairs will present an optimal comprehensive friction and wear performance. Hopefully, the present work will provide a fundamental understanding and solid support for systematically designing the tribo-pairs in pneumatic downhole tools under practical working conditions.