On-line accurate measurement for the polished rod load of the beam pumping unit is a key technology for well pump indicator drawing and operation analysis. The precision of indirect measurement methods, such as vibration of rod liquid column and motor parameters, is low. The main problems include poor engineering application and poor stability of the load sensor direct measurement method affected by aging fatigue of material. To address these issues, a new method for soft-sensing of the polished rod load using input electrical parameters is proposed. This method firstly formulates a new mathematical model of the pumping unit′s torque factor by directly replacing the crank angle with the beam inclination angle. Secondly, it establishes the correlation among the motor input electrical parameters, the parameters of the pumping unit′s four-link mechanism and the pumping unit polished rod load. Finally, the collected motor input electrical parameters are substituted for calculation, the singular mutation values are eliminated by the Chauvenet Criterion, and the mean filter method is used to further improve calculation. After modification, the on-line measurement of the polished rod load is obtained. Engineering experiments and application results show that the method has an average relative error of 3. 87% , which shows the features of high accuracy, good stability and strong engineering practicability.