Disclosed is a solid acid catalyst for preparing D-galactose and a preparation method thereof. The method includes: S1. synthesis of a skeleton carrier: S11. preparation of a sodium aluminate solution and an organic template solution; S12. mixing the sodium aluminate solution with the organic template solution, and thoroughly shaking a resulting mixture to obtain a mixed solution; S13. adding a zirconium source to the mixed solution obtained in S12, and thoroughly mixing; S14. subjecting a reaction system obtained in S13 to a hydrothermal reaction to obtain a mixed crystal ZrO2/Al2O3; and S15. rapidly heating the mixed crystal ZrO2/Al2O3 obtained in S14 until the organic template is completely ashed, and washing a resulting product with absolute ethanol to obtain a white solid ZrO2/Al2O3; and S2. soaking the skeleton carrier obtained in S1 in concentrated sulfuric acid such that sulfonyl is loaded on the skeleton carrier to obtain the target solid acid.