In view that large top torque and negative torque are produced when crank balance (primary balance) is adopted, we present the secondary balance of beam pumping unit.

And I call the torque that is in the blackboard, I call that my positive direction, and the torque that is out of the blackboard, I give that a negative direction.

Compared with conventional beam pumping unit, the swing-rod beam pumping unit can reduce the maximum crank axle torque markedly, reduce and even eliminate negative crank axle torque.