Abstract: It is suggested that the content of Np( Ⅲ, Ⅳ )or Np(Ⅴ,Ⅵ)can be analysed, which is based on the studing the different carrier quantity for the various valency of Np using LaF_3 carrier method. At a certain condition:2.0 mol/l HNO_3-0.05mg/ml K_2Cr_2O_7acting as supporting oxident Np( Ⅲ ) and Np(Ⅳ)can be qrantitat ively coprecipitated with LaF_3, but Np(Ⅴ) and Np(Ⅵ ) can be hardly even coprecipitated. From these, the content and percentage for Np(Ⅲ, Ⅳ ) or Np ( Ⅴ, Ⅵ ) can be respectively determinated.