The invention discloses a C10+ heavy aromatic hydrocarbon selective hydrogenation ring-opening catalyst and a preparation method thereof. The catalyst includes, by mass, 50-80% of HY molecular sieve,0.05-0.35% of platinum, and the balanced being Al2O3, wherein molar ratio of SiO2 to Al2O3 is 8-13, the specific surface area of the catalyst is 450-600 m<2>/g and pore volume is 0.35-0.7 cm<3>/g. Thepreparation method includes: performing composite modification on the HY molecular sieve with ammonium fluorosilicate and a platinum solution, performing extrusive molding with the Al2O3, drying androasting a semi-product, finally performing equivalent-volume impregnation with the platinum solution, and drying and roasting the product. The catalyst has higher heavy aromatic hydrocarbon lightening activity and stability, and is especially suitable for selective hydrogenation ring-opening on large-molecular heavy aromatic hydrocarbon in poor quality to co-produce light BTX aromatic hydrocarbonor high-octane number gasoline.