This paper investigates the global stability of welded singly symmetric I-shaped beams fabricated from Q460GJ steel, a typical high-performance structural steel. Experimental tests and numerical simulations were carried out on a total of eight laterally unrestrained steel beams under a concentrated point load. A special loading system was designed through which the beam could develop lateral deflections at the mid-span. Load-displacement curves and strains of beams were measured during testing. In the finite element model, initial geometric imperfections and residual stresses were considered. The model was verified through comparisons with experimental results, and parametric studies were conducted to investigate the effects of non-dimensional slenderness and height-to-width ratio. Meanwhile, design curves for lateral-torsional buckling of welded singly symmetric beams were calculated from GB50017-2003, GB50017-201X, Eurocode 3 and ANSI/AISC360-10. Comparisons between numerical results and design curves suggested that the design methods in GB50017-2003 and ANSI/AISC360-10 were unsafe for Q460GJ steel beams while GB50017-201X and Eurocode 3 could provide reasonably conservative results for global buckling design of singly symmetric Q460GJ steel beams.