Effect of pre-ablation laser parameters on the spectral enhancement of 532 nm/1064 nm orthogonal pre-ablation dual-pulse laser induced breakdown spectroscopy (DP-LIBS) is analyzed by the spectral intensity variation of Cr I 520.8 nm and Fe I 522.7 nm for the alloy steel, and the experimental conditions are optimized. The experimental results show that DP-LIBS has a maximum spectral enhancement at the conditions of the pre-ablation pulse energy of 70 mJ, the main ablative pulse energy of 100 mJ, the distance of focus point of the pre-ablation pulse to the sample surface of 1 mm and to the main ablation pulse light path of 1 mm respectively. The spectral enhancement of Cr I 520.8 nm is 12.5 at interpulse delay time 30 μs, then decreases rapidly. Finally, the spectra enhancement mechanism of orthogonal pre-ablation DP-LIBS is analyzed.