The behavior and mechanism of extraction of Palladium(Ⅱ)with unsymmetrical sulfoxide BSO were studied. The results show that the percentage extraction of Pd(Ⅱ) achieves 99.8% from 0.1 mol·L-1 HCl media with 0.3 mol·L-1 BSO-kerosene (their phase ratio 1:1) as an extractant after 5 min extraction vibration. The structure of the complex was discussed by slope analysis method and FT-IR spectra. When HCl concentration is less than 0.3 mol·L-1, BSO acts as a neutral ligand coordinated with Pd(Ⅱ) and the composition of complex is [PdCl2·2BSO](0). When HCl concentration ranges from 1.0 mol·L-1 to 4.0 mol·L-1 , the reaction of extracting of Pd(Ⅱ) is acid ion association extraction and the composition of complex may be [H+·hH2O·(BSO)2]2·[PdCl42- ] (0)