Terahertz technology has evolved significantly over the decade, and its promising applications in imaging and security have driven substantial research into terahertz sources and detectors. However, research on terahertz functional devices remains limited. The performance of current terahertz functional devices is constrained by processing complexity, high insertion loss, and low modulation depth, which impede the broader application of terahertz technology. Graphene’s tunable conductivity and the extraordinary manipulation of electromagnetic waves by metamaterials offer new avenues for designing terahertz functional devices. This paper presents a terahertz amplitude modulation device based on graphene and chiral metasurface. The device operates at a frequency of 1.25 THz and achieves a maximum modulation depth of 95% for left-handed circular polarized waves, while maintaining a transmission for right-handed circular polarized waves that is consistently above 60%.