Abstract: There are very big axial tension and compression in th casing under the deep well and large displacement well. the paper analyzed the weakest threads joint of the casing string bthe finite element method (FEM), and studied the contac pressure and the stress distribution under the API LTC axia tension and compression. the results shows that the maximu connection pressure of API LTC casing joint located in the mal threads root, the contact pressure and stress of the front fou threads is greater than any others. The threads gluing an yielded failure possibly occurred. It has an important signifi cance to select the API LTC casing correctly for the deep wel and large displacement well.

Key words: FEM, casing threads, axial load, stress