Extraction and separation of yttrium in chloride medium using tri-n-octylmethylammonium(2-sec-octylphenoxy) acetate([N_(1888)][SOPAA]) as an extractant were studied in this article. Tri-n-butyl phosphate(TBP) was used as a phase modifier to accelerate phase separation and improve the stability of organic phase. The addition of TBP contributed to shortening phase separation time, increasing extraction capacity of rare earth elements(REEs) and decreasing viscosity of organic phase. The slope analysis method and infrared spectroscopy were conducted to investigate the ion-association extraction mechanisms. Extraction and stripping performances of the different systems were also compared. The article showed that the extraction performance of mixed [N_(1888)][SOPAA] and TBP is superior to that of [N_(1888)][SOPAA] for heavy rare earth element(HREE). Extraction and separation of yttrium in chloride medium using tri-n-octylmethylammonium (2-sec-octylphenoxy) acetate ([N_ (1888)] [SOPAA]) as an extractant were studied in this article. ) was used as a phase modifier to accelerate phase separation and improve the stability of organic phase. The addition of TBP contributed to shortening phase separation time, increasing extraction capacity of rare earth elements (REEs) and decreasing viscosity of organic phase. The slope analysis method and infrared spectroscopy were conducted to investigate the ion-association extraction mechanisms. Extraction and stripping performances of the different systems were also compared. The article showed that the extraction performance of mixed [N_ (1888)] [SOPAA] and TBP is superior to that of [N_ (1888)] [SOPAA] for heavy rare earth element (HREE).