Abstract: When running the casing string in horizontal well, there exists a high risk of getting stuck, i.e., the casing string is borne with axial pulling-pressing loads due to the "lifting up and falling down" operation mode.Accordingly a study is conducted with the Φ139.70 mm×10.54 mm N80 API LC connection as a sample.The applicability of the said connection to the horizontal well service is evaluated via the FEA numerical simulation and the full-scale physical simulation test.As a result it is identified that when applying the very type of connection to the horizontal well, there comes a risk of leakage due to the rather large repeated pulling-pressing loads as borne thereby.