Abstract: A thermodynamic equilibrium model consisted of multi-metal ion and low molecular weight ligand was constructed to study the speciation of Pu⁴⁺ in human blood plasma and the influences of concentrations of DTPA, CO^2-₃and Citrate^3- on the speciation. Computer simulation indicates that low concentration of Pu⁴⁺ in blood plasma with Pu(OH)₄(l) speciation accumulates in liver. Pu⁴⁺ form precipitation is difficult to eliminate from the body under the high concentration of Pu⁴⁺ in plasma fluids. When the concentration of DTPA is 2.5×10^-5 mol/L, the species of plutonium is mainly as negatively charged Pu(OH)DTPA^2- and maintains stable. The species was at first calculated at pH 5.0, with the increase of concentration of Citrate^3-, the major speciation of Pu⁴⁺ is as PuCitrate2^2- and PuCitrate⁺ which are excreted easily from body. In blood plasma Pu⁴⁺ combines with Ca²⁺ and Mg²⁺ to form CaHDTPA^2-, Ca₂DTPA^-, CaDTPA^3-, MgHDTPA^2- and MgDTPA^3- when the concentration of DTPA is 4.6×10^-5 mol/L, which excrete Pu⁴⁺ and produce toxic side effects on bone at the same time.