Abstract: <b<Objective</b< To evaluate the value of CT in the measurement of long bone. <b<Methods</b< More than 600 cases of humerus fracture, femur fracture and tibia fracture were confirmed by X-ray examination, while 302 cases were operated with internal fixation by intramedullary pin. CT location scan had been done on the healthy bone before the operation so that we could measure the length of the diaphysis and the width of the narrowest marrow cavity. <b<Results</b< The intramedullary pin that we elected according to the data of CT location measurement adjusted to the operation. <b<Conclusion</b< The technology of CT location scan can provide the precise measurement data for the clinic.