Abstract: The arc-ultrasonic could be excited by modulating the plasma arc through high frequency.Adding Ti-6061Al as filling material,the effect of arc-ultrasonic on microstructure and mechanical properties of joint of SiCp/6061Al composite in plasma arc “in-situ” alloying welding(PAW) was studied.And then it was compared with conventional PAW.The results show that to compared with conventional PAW,arc-ultrasonic could significantly refine the joint microstuctrue.TiN and TiC particles distributed more dispersively,and no brittle phase Al4C3 and defects such as pores and cracks had been found.The arc-ultrasonic made the hardness of the weld middle zone become lower and the strength of welding joints increased to 252 MPa,which was increased by 7% than that of conventional PAW.The number of dimple in the tensile fracture significantly increased,taking remarkable features of the ductile.