Abstract: A coupled dynamic model for describing the dynamic performance of the polished rod load of beam pumping units was established. The multi-degree-of-freedom spring-quality-damper mechanical dynamic system was adopted to describe the vibration characteristic of the sucker rod string. The compressibility of the gas in the pump barrel， the changing pressure in the pump barrel and local resistance of the pump valve were comprehensively considered. The new equations describing the dynamic sucker rod pumping process were set up in order to determine downhole boundary conditions to solve the sucker rod string vibration model， which represented the interrelationship between the pressure in the pump barrel， the fluid flow into the pump barrel， the volume of the fluid in the pump barrel and the movement of the plunger piston. The time-stepping finite element method was employed to simulate the rod-pump coupled dynamic model. Oil field application shows the fairly effectiveness and accuracy of the new model， which can be used for the prediction of the working condition parameters such as the load， pump efficiency， torque and balance， and the fault diagnosis.

Key words: beam pumping unit, polished rod load, sucker rod string, oil pump, dynamic modeling