Abstract: The casing connecting thread bears both bending load and conventional load in the curved portion, which cause the casing connecting thread with higher failure rate in the curved portion than in the straight well. However, at present the mechanical behavior of casing connecting thread under bending load is indeterminate. Aiming at this issue, a 3-D mechanical model of the connecting thread is established and calculated by the finite-element analysis software based on the principle of virtual work, contact nonlinear theory and Von Mises elastic-plastic criteria, to obtain stress distribution of the casing connection thread. The comparison of numerical simulations and experimental results illustrates the validity of the model. On that basis, the parameter sensitivity of the taper, angle of bearing surface, angle of oriented surface, tooth depth and screw pitch are analyzed, and the influence of each parameters to the stress distribution under bending load is concluded. This paper provides the science basis to optimal designing, and it has important project significance on reducing the failure rate of casing connecting thread.