<p>Crack damage in directionally solidified nickel-based superalloys severely threatens the reliability of aero-engine components. This study proposes a brazing repair method assisted by water-guided laser pretreatment to enhance repair quality. The effects of different pretreatment methods and laser parameters on microstructure evolution and mechanical properties of brazed joints were systematically investigated. Results show that water-guided laser pretreatment effectively removes surface oxides and contaminants while generating a refined remelting layer on the substrate. This modified surface significantly improves the wettability of the molten filler metal and promotes metallurgical bonding at the interface. During brazing, intensive elemental diffusion occurs between the filler metal and substrate. The diffusion of melting-point depressants (B and Si) into the substrate increases the liquidus temperature of the residual liquid, inducing γ-Ni solid solution nucleation and growth from the substrate toward the brazing center. Upon further cooling, eutectic reactions form structures comprising γ-Ni, CrB, and Ni₃B phases. Mechanical testing demonstrates that optimized water-guided laser pretreatment significantly enhances shear strength and interfacial bonding quality of brazed joints. The improved performance is attributed to the regulated remelting layer, enhanced elemental diffusion, and controlled phase evolution during brazing. This study provides an effective strategy for high-quality repair of directionally solidified nickel-based superalloy components and offers insights into the brazing repair mechanism assisted by water-guided laser pretreatment.</p>