Abstract: To improve issues such as mechanical property degradation and nitrogen escape during arc additive manufacturing of high-nitrogen steel (HNS), additive manufacturing experiments of HNS were conducted under ultrasonic frequency pulsed gas metal arc (UFP-GMA) and pulse gas metal arc (P-GMA) processes, and the effect of ultrasonic frequency pulsed current on the microstructure and mechanical properties of HNS additive manufacturing components was analyzed. The research results indicate that the microstructures of the HNS additive manufacturing components under both processes are composed of dendritic ferrite and an austenite matrix. Due to variations in heat dissipation direction and temperature gradient, the ferrite microstructure transforms from long dendrites to short dendrites, and the growth direction exhibits multidirectionality. The superimposed ultrasonic frequency pulsed current can generate a high-frequency vibration effect, fragment dendrites, refine grains, and transform the dendritic crystals at the interface into equiaxed grains. Compared with the conventional pulsed GMA additive manufacturing process, the mechanical properties are improved after superimposing the ultrasonic frequency pulsed current; the tensile strength in the lap direction is 987.1 MPa, which is increased by 7.1%; the tensile strength in the deposition direction is 970.6 MPa, which is increased by 6.2%; the microhardness is 350.3 HV. The fracture modes under both processes exhibit typical ductile fracture characteristics. A second phase, which is a Cr-Mn-Fe oxide, precipitates in the dimples, causing the precipitation of Mn element and a decrease in mechanical properties.