Abstract: Reprocessing of spent fuel based on supercritical fluid extraction was intensively studied for its promising potential to reduce the secondary liquid waste generated. In this study, complexing extraction of neodymium nitrate hydrate in supercritical carbon dioxide containing tr-n-butyl phosphate (TBP) was investigated, more than 97% of the extraction efficiency was obtained. Effects of different particle sizes, TBP flow rates, temperature and pressure on the extraction efficiency were studied and discussed. It was assumed that the kinetics of the complexing extraction process was controlled by compexing reaction. A kinetics model was proposed to describe the extraction process.