Abstract: Ultra-high density drilling fluid dispersant JZ-1 was synthesized by graft copolymerization of natural materials and vinyl monomer. The effects of molecular weight regulator, AMPS and raw materials ratio on the dispersant properties were studied. Copolymerization was characterized with IR. Thermal stability of copolymer was measured by thermal analysis. Barite surface potential was studied by Zeta potential instrument. The mud properties of copolymer as dispersant for drilling fluids were evaluated in laboratory. The experimental results showed that funnel viscosity decreased from 282 s to 130 s when 2% JZ-1 were added to the drilling fluid with the density of 2.8 g/cm³, and the rheology behavior and sedimentation stability of drilling fluid were improved significantly.