Abstract: ²³⁷Np is one of the key nuclides in non-α process of high level liquid waste because of long half-life and high biotoxicity. In this work, the effects of extractant concentration, initial nitric acid concentration and temperature were studied for Np(Ⅳ), Np(Ⅴ), Np(Ⅵ) extraction process. The result shows that the increasement of concentration of N,N′-dimethyl-N, N′-dioctyl-3-oxa-glutaramide(DMDODGA) and initial nitric acid can enhance the distribution ratios of Np(Ⅳ), Np(Ⅴ), Np(Ⅵ). When the concentration of DMDODGA is lower than 0.005 mol/L, 1∶2-type complexe is found for Np(Ⅳ). When the concentration of DMDODGA is higher than 0.005 mol/L, 1∶3-type complexe is found for Np(Ⅳ). 1∶2-type complexe is found for Np(Ⅴ) and Np(Ⅵ), when the concentration of DMDODGA is in the range of 0.1-1.0 mol/L. The extractions between DMDODGA and Np(Ⅳ), Np(Ⅴ), Np(Ⅵ) are exothermic reactions. The enthalpy changes are -5955 kJ/mol, -22.02 kJ/mol and -31.40 kJ/mol, respectively. The decrease of temperature is benefit for the reaction.