The evolution of integrated optoelectronic devices has transitioned from conventional two-dimensional configurations to full spatial dimensions. Laser direct writing, with its unique three-dimensional processing capabilities, has significantly contributed to the advancement of photonic chips. Lithium niobate has garnered considerable interest due to its excellent material properties. Nonetheless, the large refractive index mismatch at the interface between lithium niobate and air considerably affects the accuracy of laser direct writing within lithium niobate crystals. Adaptive optics-based aberration correction emerges as a practical approach to address this challenge. In this study, we begin with an analysis of the point spread function and proceed to derive theoretical precompensation functions. In experiments, we employ a spatial light modulator to implement aberration correction. We systematically compare and characterize grating structures processed with and without aberration correction. Employing aberration correction at a depth of 110 μm beneath the surface results in the formation of uniform laser-modified structures devoid of focal subpoints. The incorporation of adaptive optics into the laser direct writing process paves the way for the fabrication of high-quality three-dimensional photonic structures within lithium niobate crystals.