Abstract: Based on the power-running data of the fuel recycle of the LingAo II project, the uncertainty of the design parameter of AFA 2G fuel assembly is calculated, analyzed and evaluated by FRAMATOME's COCCINEL computer code. Though the AFA 2G fuel assembly have been used for a long time, and is gradually replaced by AFA 3G and Alliance fuel assemblies, but the researched results from AFA 2G is also suitable for the new type fuel assemblies. As a series of products from the same company, the three fuel assemblies have some commonness in some way. So, the research on the uncertainty of the design parameters of the fuel assembly is representative for us.