Abstract: It is one of main content for engineering to estimate effect of casing damage. Technology of 36- finger image caliper can judge bend, changing diameter, distortion of casing. The article introduces logging instrument of 36-finger image caliper and interpretation method and also gives examples. Based on forcedly contact, 36-finger image caliper can offer 36 curves of well diameter, so the effect of casing damage is given. Interpretation figures are nice and vivid, including solid figure, image figure of well wall, section figure of well wall.