Abstract: Analysis model was established for the relationship between neutron conversion ratio and operation life. The law that yield of ⁶⁰Co and neutron conversion ratio changed with operation life of High Flux Engineering Test Reactor (HFETR) was studied by designing and calculating actual reactor cores with different operation lifes. At the same time, when reactor core loaded entirely with new fuel elements, the effect of its loading number on yield of ⁶⁰Co and neutron conversion ratio was found out. Accordingly, under the condition of balance cycle in HFETR core, loading number of fuel element was analyzed by using point reactor model. The optimization study was valuable as the reference for optimization on loading design and operation manner of HFETR in order to improve its operation economy. The results show that 25 days operation life for HFETR is preferable to any other and the ideal number of fuel element is 70 in balance cycle with the life.