Three types of Mg-based fillers with various Al-containing were applied for the tungsten inert gas (TIG) welding-brazing of MB3 alloy and Ti-6Al-4V alloy. Results reveal that coarse α-Mg grains accompanied with black precipitates of Mg17Al12 phase occurred in the fusion zone, whereas thicker TiAl3 phase was formed in the brazing zone with the increasing Al-containing from filler wire. The evident decline of micro hardness was observed in the joint fusion area, owing to the comprehensive effect of grain growth and Orowan hardening mechanism. With optimum welding current of 65A and AZ91 filler, the sound Mg/Ti joint with joining strength of 202 N mm−1 was obtained. Eventually, the formation of interfacial layer was analyzed to further reveal the joining mechanism of Mg/Ti joint.