To reduce significantly the leakage of 4,4',(5')-di-(tert-butylcyclohexano)-18-crown-6 (DtBuCH18C6), an improved silica-based polymeric composite, (DtBuCH18C6+TBP)/SiO2-P, was prepared. It was done by impregnating and immobilizing DtBuCH18C6 and tri-n-butyl phosphate (TBP) molecules into the pores of SiO2-P particles through an advanced vacuum sucking technique. The adsorption of 10 typically simulated elements, Ru(III), Pd(II), Ba(II), Mo(VI), La(III), Y(III), Na(I), K(I), Sr(II), and Cs(I), toward (DtBuCH18C6+TBP)/SiO2-P was investigated in the HNO3 concentration range of 0.1-5.0 M. In optimum 2.0 M HNO3 solution, (DtBuCH18C6+TBP)/SiO2-P showed strong adsorption ability and high selectivity for Sr(II) over all of the tested elements. The quantity of total organic carbon (TOC), 281.8 ppm, leaked from (DtBuCH18C6+TBP)/SiO2-P was much lower than that of 532.3 ppm leaked from DtBuCH18C6/SiO2-P. A significant reduction of DtBuCH18C6 leakage was achieved. In terms of the batch experiments, the chromatographic separation of Sr(II) from a 2.0 M HNO3 solution was performed by a (DtBuCH18C6+TBP)/SiO2-P packed column. Na(I), K(I), Cs(I), Pd(II), Mo(VI), La(III), Ru(III), and Y(III) were found to elute facilely and flow into the effluent along with 2.0 M HNO3 because of the weak or no adsorption. Sr(II) and Ba(II) adsorbed strongly and were desorbed sufficiently by distilled water and then separated completely from the others. The recovery percentage was 100.5% for Sr(II) and in the range 99.2-100.6% for the others. The application of the macroporous silica-based (DtBuCH18C6+TBP)/SiO2-P polymeric composite in partitioning of Sr(II) from high level liquid waste (HLLW) is promising.