Abstract: The casing string leaked during pressure test in one well, and then the operation by imaging behind casing (IBC) was performed to check casing string.The leakage cause was analyzed on the basis of IBC results.It was considered that the leakage of casing string was related to wear by analyzing the effect of wear on resistance to leakage.Based on analysis of IBC principle, it was found that IBC technology could give possible leakage position where the casing was worn severely, but could not determine the location of small crack penetrated on casing.It was thought that the oval deformation occurred in casing string, that was related to worse cementing quality and nonuniform load on casing string by analyzing the effect of cement quality on service life of casing string.