[en] Activity determination of ^89,90Sr in HLLW by N,N,N',N'-tetra-isobutyl-3-oxo-glutaramide (TIBOGA) extraction-liquid scintillation counting method is described. First, actinide elements and other related elements are removed from simulated HLLW by TRPO-kerosene extraction. Then, Sr²⁺ is extracted into TIBOGA-n-octyl alcohol-kerosene phase. The above organic phase is washed by mixed solution of 0.01 mol/L Fe(NH₂SO₃)₂-2 mol/L HNO₃ in order to eliminate disturbance of Ru³⁺. Finally, activity of ^89,90Sr in the organic phase is determined by liquid scintillation counting method. The determination limit of the method is 1.7 kBq/L, the precision is 2%, the recovery is higher than 97%, respectively. Gross decontamination coefficient of related elements in simulated HLLW are as follows: >1 x 10⁶ for UO₂²⁺, Th⁴⁺, Pu⁴⁺, PuO₂²⁺, Np⁴⁺, Co²⁺ as well as Cs⁺; >3 x 10⁵ for NpO₂²⁺; >3 x 10⁴ for Zr⁴⁺; ≥2 x 10⁴ for TcO₄^-, Pu³⁺ and PaO₂⁺; > 3 x 10³ for Ru(NO)³⁺; >1 x 10³ for RE; > 7 x 10² for Am³⁺