Abstract: The process and mechanism of the ligand volume controlled Pd(PR₃)₂ (PR₃=PH₃, PMe₃, and PtBu₃) oxidative addition with aryl bromide were investigated, using density functional theory method with the conductor-like screening model. Association pathway and dissocia-tion pathway were investigated by the comparison of several energies. The cleavage energy of Pd(PR₃)₂ complex was calculated, as well as the oxidative addition reaction barrier energy of Pd(PR₃)_n (n=1,2) with aryl bromide in N,N-dimethylformamide solvent. This study proved that the ligands volume possessed a great impact on the mechanism of oxidative addition: less bulky ligand palladium associated with aryl bromide via two donor ligands,but larger bulky ligand palladium coordinated via monoligand.