Abstract: The connection-surface damage of the acoustic system in an ultrasonic plastic welder is analysised. It is shown that the horn made of aluminum alloys(e.g.Ly12CZ) is apt to adhesion-wear,that makes the resonance properties worsening and leads to decreasing of the acoustic transmitting efficiency.The surfaces are treated using nitrogen plasma immersion ion implantation. After treatment alternatively with high voltage and low voltage implantation, the surface microhardness is increased by 60% and AlN phase precipitates in the near surface. Consequently,it substantially decreases the tendency of the adhesion-wear.