Abstract: Objective According to the growing demands for higher welding efficiency and quality of thick EH40 steel plates in shipbuilding, this study aims to investigate the effects of different groove shapes on narrow-gap TIG welding, and evaluating their welding efficiency and joint mechanical properties. Methods The double U-shaped and X-shaped symmetrical groove forms are designed, and multi-layer and multi-pass narrow-gap TIG welding process is to weld the EH40 steel with a thickness of 60 mm. Influence of different weld groove shapes on welding efficiency is analyzed by comparing the number of passes, filler metal consumption, total welding time and arc voltage stability. Tensile, impact and bending tests, along with microstructural examinations, are performed on the resulting welded joints. Results Compared with the X-groove, the double U-groove significantly reduced the number of weld passes, filler metal consumption and welding time, enhancing overall efficiency by approximately 34%. The double U-groove also exhibited more stable arc voltage with less fluctuation. Microstructural observation shows that the weld zone and HAZ of groove shapes are mainly ferrite and pearlite with uniform distributions. The double U-groove produces higher tensile strength, reaching above 595 MPa, and both grooves maintain impact energy values above 150 J, no cracks are observed in bending tests. All welded joints satisfies the requirements of the China Classification Society (CCS). Conclusion Compared with the X-groove, the double U-groove demonstrates superior welding efficiency and mechanical performance in narrow-gap TIG welding of thick EH40 steel, confirming its potential application in the high-demand shipbuilding industry.