Abstract: A femtosecond laser high-speed scanning method is used to prepare hierarchical micro-nano structures on the surface of fused silica. One-scale is periodic micro-nano structure, two-scale is the ablation groove and triple-scale is the gridding structure comprised by bi-direction grooves. The mechanism of micro-nano structure fabricated by femtosecond laser scanning at high speed was revealed through numerical calculations. The wettability test shows that micro-nano structure with the period of 400～500nm which obtained under 1 MHz, 1 000 mm/s, 55% peak power and 30 μm the orthogonal groove spacing has the best wettability. The contact angle of Bi₂O₃-50%B₂O₃ solder can be reduced by 8° than that of unmodified fused silica which is beneficial to reduce the residual stress of the brazed joint.