Abstract: The feasibility of application of slightly enriched uranium （SEU） in CANDU reactor of Qinshan Phase III NPP under the time-averaged equilibrium refueling was studied in this paper using the code system DRAGON/DONJON. The optimum enrichment of Qinshan CANDU reactor was determined to be 1.125wt%. The instantaneous SEU reactor core was calculated and inspected based on the patterned channel age model. It is shown that the simple 2 burnup zones, 2/ and 4-bundle-shift refueling scheme will satisfy the license limits of the maximum bundle power and channel power, which are 935KW and 7300KW respectively. It was estimated that using this optimum enrichment SEU in Qinshan Phase III will increase the burnup to 18.5GWd/tU, save 53 tons of natural uranium resource, decrease the spent fuel to be disposed to 116 ton and obtain 8.15M$ benefit annually. The transition from the nature uranium （NU） to the slightly enriched uranium （SEU） can be completed without major modification of the structure of reactor core and operation mode. This strategy has significant practical and economical benefit.