Abstract: As a new technology in the petroleum industry, Expandable Tubular Technology (ETT) is being paid more and more attentions. By applying this technology, casing program can be improved and hole size can be enlarged, and it is also favorable for the following drilling and production operations. Limited element simulation method is used to study the difficulties of ETT, i.e., the expansion cone and connection thread. An expansion cone model and the connection thread are designed, and the geometry profile, size and cone angle, as well as the type, shape, sealing face and torque shoulder are also determined. Field tests of ETT in two wells proved its reliability, and it’s a novel solution for casing program simplification, downhole troubles minimization, completion hole size enlargement and casing repair.