Abstract: To clarify the effects of the shoulder on the load bearing of connection threads, FEM models are built based on φ139.7 mm FH connection under four conditions, i.e. no shoulder, only primary shoulder, only secondary shoulder and double shoulders, respectively, and analyzed the mechanical properties under complex loads. Research results showed that the primary and secondary shoulders could play vital roles for ensuring the stability while making up connections; the primary shoulder can make the pin connection generating tensile effects under pre-tightening torsion, whereas the secondary shoulder can make the pin connection produce compressive pre-tightening effects, which, eventually, will affect the load bearing characteristics and ultimate torsion resistance. Under the same axial tension, the ultimate torsion resistance with only secondary shoulder is 12% higher than that when it has only primary shoulder, whereas the double-shoulder connection is 69% higher than when it has only a primary shoulder connection. Research results could provide references for development and the structure design of a new high-performance drilling tool connections.