Abstract: The laser-ablation threshold of aluminum alloy was accurately measured by dual-wavelength dual-pulse laser-ablation laser-induced breakdown spectroscopy under orthogonal geometric arrangement. For 532 nm laser wavelength and 12 ns laser pulse width, the laser-ablation energy threshold of aluminum alloy was determined to be 48 J, equivalent with a fluence threshold of 9.8 J/cm2, under tightly focused condition with an aspheric lens of 2 cm focal length. This is a new spectroscopic method to measure laser-ablation threshold. It is more sensitive and more accurate in comparison with established methods for laser-ablation threshold measurement, and the measurement is rapid and quite convenient. This method can be used for accurate laser-ablation threshold measurement for different materials.