Seed oil is a momentous agronomical trait of soybean targeted by domestication in breeding. Although multiple oil-related genes have been uncovered, the knowledge of regulatory mechanism of seed oil biosynthesis is currently limited. We demonstrate that seed-preferred gene GmZF351 encoding tandem CCCH zinc finger protein is selected during domestication. Further analysis shows that GmZF351 facilitates oil accumulation by directly activating WRI1, BCCP2, KASIII, TAG1 and OLEO2 in transgenic Arabidopsis seeds. Overexpression of GmZF351 in transgenic soybean also activates lipid biosynthesis genes, thereby accelerating seed oil accumulation. ZF351 haplotype from Glycine max group and Glycine soja subgroup III correlates well with high gene expression level, seed oil contents and promoter activity, suggesting that selection of GmZF351 expression leads to increased seed oil content in cultivated soybean. Our study provides novel insights into the regulatory mechanism for seed oil accumulation and manipulation of GmZF351 may have great potential in improvement of oil production in soybean and other related crops.