Flexible drill pipe has become an important tool for old well reconstruction and production increase and efficiency improvement.In order to ensure the reliability of the spherical seal of flexible drill pipe,numerical simulation and experimental research were carried out on a designed O-ring spherical seal structure.Based on ANSYS finite element analysis software,the effects of sealing clearance,fluid pressure,rotation angle and whether there is a retaining ring on the sealing characteristic parameters such as von Mises stress,contact stress and effective sealing width of O-ring were investigated.The results show that there is a coupling relationship between fluid pressure and sealing clearance,and the higher the fluid pressure,the smaller the sealing clearance is required.Reciprocating rotation will lead to an increase in the maximum von Mises stress and maximum contact stress,and the impact will increase as the seal gap increases.The installation of the retaining ring can effectively prevent the O-ring from squeezing into the gap when the sealing gap and fluid pressure are high.The reliability of the O-ring spherical sealing structure is verified through indoor tests,which provides a theoretical basis and technical support for field applications.