Abstract: The Eucalyptus urophylla seedling seed orchard used in this study was established based on backward selection involving 45 families within 7 provenances.Results showed that there were highly significant differences in growth and stem form,rate of blossoming and other characters among families and provenances at the age of 3.The growth,stem form and tree crown of Eucalyptus urophylla were moderately or strongly hereditary at provenance,family and individual levels,and genetic coefficient variance of characters were minor by age increasing,and provenance heritablityfamily heritablityindividual heritablity.Thirty-eight families(84.4% of the total) in SSObs produced higher stem volume than those of the control No.1(CK1),and 39 families(86.7%) were better than the control No.2(CK2) regarding the stem volume.These results showed that most of the parent materials in the SSObs had ideal genetic properties.Information obtained from estimating the breeding value of family and individuals in family using BLUP method,and from the selection of ideal families and individuals,provided valuable evidence for the genetic thinning management of SSObs.The genetic structure of E.urophylla in SSObs was considered to be the genetic mode of additive gene + dominate gene.This result was vital for the management of the SSObs by thinning the inferior and reserving the superior.