Abstract: The generation and transmutation process of the transplutoniums in the conversion chains for 252 Cf production is calculated and analyzed. The production and conversion efficiency of the chains with different target nuclides and neutron spectrums including fast, thermal and moderated neutron spectrums is computed. The efficiency and the advantages and disadvantages of the conversion paths for 252 Cf under different neutron spectrums and neutron flux levels are analyzed. The multi-group depletion program STEP1.0 based on linear chain method is used to calculate the nuclide densities. The differences of the conversion efficiency caused by the neutron spectrum can be qualified more accurately with the multi-group cross section calculations. The higher conversion efficiency than the typical thermal neutron spectrum can be obtained by some moderated spectrum optimized for absorption reaction through the irradiation of some transplutoniums（242Pu, 244 Cm, 246Cm）.