The ball-disc friction experiments are performed by applying the YG8 cemented carbide ball and the aluminum alloy 7050-T7451 plate under high speed and high load, and then the wear depth of the groove was observed using white light interferometer. The average contact normal stress was calculated by the depth of the groove. The relationship between friction coefficient and average contact normal stress as well as sliding velocity is fitted with Minitab. It shows the friction coefficient decreases with the increasing of the sliding velocity and the average contact stress. The results provide certain theoretical basis to build the friction model and finite element model of machining Al alloy.