Abstract: According to the data casing failure from oilfield, and casing failure as top event, the fault tree of the casing was established in the paper, the model included 47 different essential events. By analyzing the fault tree of casing, 27 one-order minimum cut sets, 29 two-order minimum cut sets and 1 four
-order minimum cut sets of the fault tree were obtained. The casing failure is collapse, fracture and serious corrosion, finally the paper presents some measures of improving reliability of the casing.

Key words: casing, reliability, fault tree, essential event