High-accuracy measurement of force affects real-time control and process adjustment of industrial production. Piezoelectric sensor can be applied to measure force with the characteristics of high frequency and stiffness, great dynamic response and resistance to harsh conditions. As an important part of test, calibration determines sensitivity coefficient which directly affects test accuracy. To improve the calibration accuracy of offset loading force for multi-sensor piezoelectric dynamometer, a novel calibration method using sensor sensitivity difference is proposed in this paper. The calibration experiments of four sensors are performed to obtain the axial sensitivities and the force-to-electricity conversion coefficients. The multiple loading points (MLP) calibration experiments of dynamometer are carried out, and the calibration results prove that the sensitivity difference of four sensors is the main reason affecting the calibration accuracy. The sensitivity difference calibration method (SDCM) is applied to the MLP calibration experiments, and the results show that the average resultant force deviations are reduced from 418.79N (8.38% FS) to 24.16N (0.61% FS) under a loading force of 5000N, which proves high accuracy and reliability of SDCM. The calibration method will provide guidance for improving the calibration accuracy of dynamometer.