Abstract: To improve economic efficiency during the physical start-up of China Experimental Fast Reactor (CEFR), the feasibility of using secondary neutron source to replace ²⁵²Cf source was studied. The secondary neutron source was designed based on the principle of neutron generation of secondary source and with reference to relevant CEFR parameters. ¹²³Sb (n, γ) reaction rate and ⁹Be single nucleon (γ, n) reaction rate in the secondary source assembly were calculated by using MCNP code, and source strengths in different exposure conditions were obtained. Then the feasibility of applying the secondary source in CEFR physical start-up was analyzed. The calculation results show that the designed secondary neuron source assembly can meet the requirements of CEFR start-up in most operating conditions. The secondary neutron source designed in this paper and the calculation results can provide useful data for the application of secondary neutron source in CEFR start-up.