The invention discloses an anti-seepage construction method built on a sandy gravel foundation for a cemented gravel dam body. The method comprises the steps that S1, a foundation cushion layer with an anti-seepage effect is laid through rich-slurry cemented gravel; S2, a high-power flat vibrator is adopted for tamping the lap joint part of an anti-seepage layer and a rolling body; S3, the cemented gravel is vibrated by adding slurry to serve as an upstream anti-seepage layer; S4, rich-slurry cemented gravel materials are poured on the two sides of a grid plate of an asphalt grid plate partingjoint, and after the anti-seepage layer is constructed to the dam crest, a nitrile elastomer is mounted in a horizontal construction joint of the rich-slurry cemented gravel anti-seepage layer to stop water; and S5, the rich-slurry cemented gravel is adopted for rolling on the upstream sandy gravel foundation face, cement paste is sprayed, and a horizontal foundation anti-seepage layer is formed.The cemented gravel dam is built on the sandy gravel foundation, the problem of seepage caused by incomplete separation of aggregate and mortar in the construction process of the cemented gravel damon the sandy gravel foundation is effectively solved, the construction method is simple and easy to operate, and the three-dimensional anti-seepage effect can be achieved.