Abstract: The welding test on plate without wire filling and butt welding test of X80 pipeline steel were carried out by using ultra-high frequency pulsed TIG welding, and the influence of ultra-high frequency and duty ratio on the weld formation was studied, including penetration, weld width and forming coefficient. The microstructure observation and mechanical property test of the butt welded joint were carried out. The results show that with the increase of pulse frequency and duty cycle, the penetration and width of the weld increase, and the forming coefficient decreases genarally. The microstructure of the weld zone is mainly needle ferrite and granular ferrite, the microstructure of the coarse grain zone is mainly composed of bainitic ferrite, granular bainite and a little of martenite, and the microstructure of the fine grain area is mainly composed of polygonal ferrite and a small part of bainite. The tensile fracture are located at the base metal, and the tensile strength of the welded joint is higher than that of base metal, and the impact absorbing power of weld center is the lowest.