Abstract: The reduction of mechanical properties caused by internal defects,coarse grains and other factors was one of the main challenges in arc welding and additive manufacturing. Making the WAAM process supplemented by synchronized micro-area hammering and impacting would be a feasible way to solve the problem. Therefore,a micro-hammering technology based on compact and small linear actuators was proposed in the paper,which had advantages of small size,high displacement resolution,fast response speed,large output force and high frequency. The effect of synchronous hammering on the high-temperature solidification area was verified by the fixed-point welding and delayed hammering simulation,and the effect of the hammering oscillating molten pool was verified by the fixed-point welding and the hammering simulation nearby the welding point. The research result showed that after the hammering was added,grains were all refined to a certain extent,and it could be observed that coarse columnar crystals were transformed into fine equiaxed crystals. Both the hammering frequency and the hammering force had a great influence on the hammering effect.