Abstract: The diameter of connector usually is bigger than that of drilling string. Under normal conditions, the body of drilling string was not contact with the hole/casing. The mechanical model of drilling stringwith connectorswas setup in the paper, and was analyzed by iterationmethod for drag and torque during
drilling, pulling out, going down and back reaming. Themodel can predict themagnitude and direction of contact force at every connector. Compared the calculated datawith the field data, the errors of the hook load was less than 5% and that of torque was less than 7%. Thismodel offered a simple and effectivemethod for predicting the drag and torque of drilling string.

Key words: drilling string, connector, drag and torque, analysis