Abstract: The water tunnel flow visualization was conducted to investigate the flow structures of nonslender delta wings at low Reynolds number. The experiments were focused on the effect of leading-edge cross section on vortex structures for 50° sweep delta wings and on the maximum sweep angle at which the dual vortex structure exists. It is obtained that the dual vortex structures are sensitive to the dye injection location, and such structure can be observed at sweep angle as large as 64°. Meanwhile, the experimental results indicate that the leading edge cross-section significantly influences the vortex breakdown position and the trajectory of the vortex core. In comparison with the windward beveled leading edge, the leeward beveled one is easy to generate the dual vortex structure over the 50° sweep delta wing, to delay the primary vortex breakdown, and cause the primary vortex core close to the wing surface, which are benefit to improve the aerodynamic characteristics of the delta wing.