Abstract: A new method for analysis on beam pumping unit was proposed.On the basis of kinematic analysis of beam pumping unit,the general dynamics equation in the form of virtual power was applied to analyze the contribution of every part including balancing weight of a beam pumping unit to crank axle torque in consideration of inertia effects.The exact analytical expression for computing crank axle torque was obtained.According to this exact analytical expression,the effect of every part of a beam pumping unit on crank axle torque can be quantitatively studied.This method can be used to analyze all types of beam pumping units.As an actual sample,the exact analysis of swingrod beam pumping unit is given.