Abstract: Objective To explore a new method for body surface orientation of the puncture site,determination of the direction of the needling and puncture depth for caudal block.Methods Three-dimensional reconstruction of the pelvis was performed in 8 cases for measuring the distances between the sacral hiatus and the planned site of anesthetic delivery and the size of the sacral hiatus.After image processing with the technique of shaded surface display(SSD),the shapes of sacral hiatus and sacral tube were evaluated.Results Three-dimensional reconstruction of the pelvis in the 8 cases allowed clear view from any directions of the sacral hiatus and sacral tube and accurate measurement of the size of the sacral hiatus.After simulated cutting of half of the rumpbone,the distances between the sacral hiatus and the drug injeetion site were accurately measured.With these measurements,accurate preoperative localization of the puncture site on the skin was achieved and the anesthesia was successful in all the cases.Conclusions This technique can provide accurate data for localization of the puncture site on the skin and determination of the direction of the needling and the puncture depth for caudal block to increase the successful rate of anesthesia,lower the operative risks and allow simulated operative training.