Objective The family reconstruction method was used to establish paternity index algorithm for uncle-nephew relationships between two full sibling uncles and one nephew.Methods According to Mendelian genetic law,the family of two known full-sib uncles and one nephew were reconstructed according to the relationship between uncle and nephew,and the test hypothesis was established between two full sibling uncles and one nephew as the uncle-nephew relationship and unrelated individuals,and the paternity index of the uncle-nephew relationship between two full sibling uncles and one nephew was calculated by using Excel.Results Among the 99 genotypic combinations between two full sibling uncles and one nephew,91 of which were consistent with the genetic rules of uncle-nephew relationships,while 8 of which were not.a stepwise mutation model was introduced in the situations that do not conform to the genetic laws of uncle-nephew relationships.The paternity index of uncle-nephew relationship between two full sibling uncles and one nephew can be calculated using Excel.Conclusion The uncle-nephew testing involved by two full sibling uncles makes use of the role of the assistant,and the paternity index of the obtained uncle-nephew relationship is higher than that between two known full-siblings alone and their nephew,which has a good practical value in helping the appraiser to draw a clear appraisal opinion.