To provide experimental data and recommendations for the application of high-strength steels in low-temperature environments， this paper focuses on two key influencing factors： welding heat input and different delivery conditions of base metals. Two types of high-strength steels， Q550D and Q690D with thicknesses of 20mm， were selected in thermo-mechanically controlled process （TMCP） and quenched and tempered （QT） conditions. Three commonly used gas shielded welding heat inputs of 1.0 kJ·mm^-1， 1.5 kJ·mm^-1， and 1.9 kJ·mm^-1 were applied to prepare the joints. The impact toughness tests were conducted， and the results were analyzed and compared. A systematic study was performed on the Charpy impact energy and transition temperature of the base metal， weld metal， and heat-affected zone （HAZ） in butt joints under different delivery conditions. The results indicate that the effect of welding heat input on the impact toughness of various regions of the joints is insignificant， while the delivery condition significantly affects the impact toughness. Specifically， the impact toughness of the HAZ in QT steel joints is superior to that of the base metal and weld metal， whereas in TMCP steel joints， the impact toughness of the HAZ is lower than that of the base metal and weld metal. The study on the ductile-to-brittle transition temperature under controlled conditions suggests that the high-strength steels used in this study exhibit good low-temperature sensitivity.