Many clinical bone nonunion or delayed union often appear in the early stage of bone healing,but they have been always found too lately.Before X-ray films of visual changes indicates salt content inbones reaching 25%,the very early changes ofclinical significance can not be observed.This paper introduces the theory of fracture healing and the definition of bone nonunionand the significance of the basic multicellular unit(BMU)and the OPG-RANKL-RANK system in bone reconstruction.Many technologies such as ultrasonic testing,vibration analysis,mechanical impedance analysis,the bone marrow cavity imaging technologiy,high-resolution CT etc.have been reported in study on the bone,as well as early diagnosis of fracture nonunion.However,the molecular level of early diagnosis is deficiency.