Reactor internals are the key components of the reactor. They provide support and positioning for nuclear fuel assemblies.They also need to be positioned accurately and prevent fatigue damage caused by fluid vibration. Cobalt-based alloys have good properties of high temperature resistance,fatigue resistance,wear resistance and so on. They are ideal contact materials for positioning.There are many defects in cobalt-based alloy surfacing of reactor internals in a nuclear power project,which also leads to the scrap of individual parts. The wear resistance mechanism of cobalt-based alloy is introduced,and the causes of defects are analyzed from various factors of surfacing.