Brassica napus L. is a vital oil crop and exhibits notable salt tolerance, making the enhancement of this trait crucial for cultivation in saline soils. Uncovering its underlying mechanism may further heighten the salt tolerance of B. napus. In this study, we conducted a genome-wide analysis of the Root Meristem Growth Factor (RGF) gene family in Brassica species and identified BnaRGF8 as a key regulator of salt tolerance. Under 200 mM NaCl treatment, all RGF genes were induced, with BnaRGF8 showing the greatest upregulation. This response was consistently observed across 10 genotypes, indicating a universal trend in B. napus. Functional characterization revealed that chemically synthesized BnaRGF8 alleviated salt-induced growth inhibition by restoring primary root elongation and lateral root formation. Additionally, BnaRGF8 preserved membrane integrity and maintained cell division under salt stress, establishing itself as a novel anti-salt peptide in B. napus.