As one of the key parts of the impact sprinkler, the swing arm is exerted by com plex dynamic stress in the impact process. Based on the dynamic explicit softwar e ANSYS/LS〖CD*2〗DYNA, a finiteelement model for simulating the rotation of s wi ng arm around the axis and the impact between the swing arm and the sprinkler bo dy was established. Several cases under three rotational angular velocities and with or without the rubber pad fixed on the sprinkler body’s contact stop were investigated. The results indicate that under the angular velocity of 400(°)/s, t he simulated peak dynamic stress of PY140 impact sprinkler was 423MPa, wit h an error less than 05% compared with the measured result. The predicted peak d ynamic stress was located offset 15cm from the centerline of the swing arm’s rotation axis, which was the same as the measured data. The extreme dynamic stre sses of different cross sections and contact stresses increased with the increas e of the rotational angular velocity. After fixing the rubber pad, the peak dyna mic stress had an average decrease of 104% under three angular velocities, whi le the contact time had an average increase of 766%. 