Abstract: In order to solve the problem of cold cracks in ultra-high-strength steel welding, the GMAW process experiment was carried out with high-nitrogen austenitic wire with lower strength than the base metal to study the microstructure and properties of ultra-high-strength steel welded joints at different grooved angles. The results show that welded joints are well formed without cracks according to cross-section of weld, the microstructure near the fusion line is mainly acicular and lath martensite, and the weld structure is mainly austenite and ferrite dendrites surrounded by austenite matrix; the average hardness of the martensite zone near the fusion line is 530 HV; the average hardness of the weld zone is 275 HV; compared to 60° grooved joints, the hardness of the martensite structure near the fusion line of 90° grooved joints are higher; The average tensile strength reaches 850 MPa, and the highest is 887 MPa, while the average tensile strength of 60° groove joints is only 690 MPa.