<p>The conventional metal inert gas (C-MIG) welding of 316L stainless steel under short-circuit transfer mode often encounters problems such as an unstable welding process and grain coarsening, which will deteriorate its mechanical properties and corrosion resistance. To address these issues, this study employed the ultrasonic frequency pulsed current assisted-MIG (UFPC-MIG) welding method to increase arc stability and facilitate microstructure refinement. The study investigated the welding process stability, weld formation, microstructure evolution, as well as the mechanical properties and corrosion resistance of the joints at various UFPC frequencies. Due to the skin effect and self-magnetic contraction effect of UFPC, the maximum width of the arc was reduced by 29.51% when the UFPC was 40&#xa0;kHz. The results demonstrated that UFPC application reduced weld width and root reinforcement defects, enhanced process stability, and increased droplet transition frequency. The stirring effect of UFPC broke the ferrite dendrites and refined the dendrite structure in the fusion zone, so that the ferrite content was reduced to 9.618% at the UFPC frequency of 40&#xa0;kHz, and its distribution was more uniform. At the same time, the grain size in the weld center area was reduced to 38.62&#xa0;μm. Consequently, the microhardness, tensile strength, elongation, and impact toughness were improved. Simultaneously, the reduced ferrite content lowered the risk of corrosion pits generation, thereby enhancing corrosion resistance in 3.5% NaCl solution. This work demonstrates that UFPC-MIG welding achieves synergistic enhancement of mechanical properties and corrosion resistance, offering a promising approach for high-performance welding applications.</p>