Abstract: The narrow gap and electron beam welding tests of 40-mm thick TA31 alloy were carried out, and defect-free welding achieved. Microstructure and mechanical properties of the two joints were compared and analyzed. The results show that the width of narrow gap welded joint is 13 mm, the microstructures of the upper and the lower of joint are evenly distributed, the weld zone consists of coarse columnar crystal, and the microstructure of the heat affected zone is similar to that of the weld zone. The width of electron beam joint is 6 mm, and the difference between the microstructures of the upper and the lower of joint are obvious. The upper part of the weld zone is the coarse columnar crystal and the lower part equiaxed crystal. Lamellarαphase is found in the upper heat affected zone, the microstructure of the lower heat affected zone is similar to that of the base metal. The microhardness peak of the narrow gap welded joint exists in the heat affected zone, and the peak of the electron beam welded joint exists in the weld zone. The impact value of the narrow gap weld is higher than that of the electron beam weld, the impact value of the heat affected zone is smaller than that of the electron beam. The impact value of the lower part of joint of the electron beam is higher than that of the upper part.