Abstract: Atmospheric plasma spraying method was used to deposit nanoscale and conventional WC-Co coatings using nanostructured WC-Co powder and conventional WC-Co powder as feedstock, respectively. Tribology properties of the coatings was investigated on a SRV under dry and water environment. Results indicate that the friction coefficient and wear rate of nanoscale coating was lower than conventional coating mostly, the wear mechanism of both coating was similar. The wear mechanism when rubbed against steel ball was mainly adhesion, brittle fracture abrasive in dry friction. In water environment, the wear of the coating was controlled by brittle flake with fatigue abrasion. When Si3N4 ball was replaced by steel ball in water environment, the friction and wear rate was effectively reduced, the wear mechanism was mainly adhesion with some abrasive. Nanoscale WC-Co coating exhibits better tribology performance than conventional coating both in dry friction and water environment. In water environment, the friction and wear can be effectively reduced when rubbing against steel ball.