Abstract: In order to analyze weldability of SiC particle reinforced aluminum metal matrix composites(SiC_p/Al MMCs), plasma arc "in-situ" welding of SiC_p/Al MMCs are carried out using argonnitrogen mixture as plasma gases and Ti-Si mixed powder as "in-situ" welded material.The results show that the dense metallurgical joining with obscure interface could be acquired by adding Ti-Si mixed powder into the pool and new composite reinforced are produced in the weld, and the needle-like phases are not found yet, ensuring the quality of joints.The mechanical testing results show that the maximum tensile strength obtained with Ti-Si mixed powder as "in-situ" material are 232.3 MPa.Furthermore the forming mechanism of porosity in welded joint and the corresponding measures are discussed.