Surface nanocrystallization is a practical approach to enhance surface wear resistance, whereas the specific mechanism of how surface nanocrystallization affects the wear resistance of NbMoTaW refractory high-entropy alloys (RHEAs) remains unclear. Herein, we performed molecular dynamics simulations to explore the wear behaviors of nanograined NbMoTaW RHEA during surface scratching. The wear resistance of nanograined models was significantly enhanced compared to the single-crystalline counterpart. As the grain size increases, the dominant plastic deformation mechanism switches from grain boundary deformation to dislocation movement. Notably, the model with a grain size of 20 nm exhibits the highest dislocation density, local stress, and degree of work hardening. At elevated temperatures, the dynamic recrystallization becomes a crucial plastic deformation mechanism and hinders the formation of dislocations, resulting in a decrease in dislocation density and consequently a decline in the wear resistance of NbMoTaW RHEAs. The current study provides insight into the mechanism underlying the enhanced wear resistance of NbMoTaW RHEAs.