Abstract: In order to improve the design of casing strength and prevent severe casing wear out,casing abrasion prediction technology was analyzed.The tension-torque equation of drill string in deep wells and extended reach wells was deduced through identifying the drill string mechanics for directional wells,and considering stiffness and buckling of drill string.The prediction model of casing abrasion was established according to the energy principle and prediction software was developed.The software can predict casing abrasion at different depths in hole,for different casing program,BHA,well track,drilling fluid types and drilling parameters,during drilling and tripping.Its application shows that the software can give a more accurate and reliable prediction,with less artificial error.It provides new technical support to ensure safe and efficient drilling of deep wells and extended reach wells.