Abstract: A novel extraction reagent, N,N,N′,N′-tetraoctyl diglycolamide(TODGA) was synthesized. The influence of various factors on the extraction of alkali earth metal from aqueous nitric acid solutions with this amide (L) and N,N-dihexyl-octamide (DHOA) is studied, including extractant concentration in n-dodecane, extracted ions concentration, acidity of aqueous phase, ionic strength of salting out agent and temperature. The composition of the extracted species and the mechanism of extraction were studied. The results suggest the extracted species to be M(NO₃)₂•2TODGA(org). The enthalpy change for the extraction of Ca(Ⅱ), Sr(Ⅱ) and Ba(Ⅱ) are （-38.85±1.37）kJ/mol, (-24.30±1.45)kJ/mol and (-9.14±2.01)kJ/mol, respectively. The ehtropy change are (-78.26±2.67)J/(mol•K), (-75.80±4.74)J/(mol•K) and (-51.85±6.11)J/(mol•K), and the Gibbs energy change are (-9.88±0.06)kJ/mol, (-2.08±0.06)kJ/mol and (6.06±0.22)kJ/mol at 293K, respectively. No emulsification or third phase formation is observed during the extraction process. On the basis of the experiment results, the method of seperation and recovery of Sr from high-level liquid waste puts forward.