A pre-stressed six-axis force/torque measurement method based on a Stewart platform was established to extend its measuring range. Compared to the traditional Stewart six-axis force/torque sensor, the principle of the pre-stressed Stewart six-axis force/torque measurement was analyzed. Then, structure design of the sensor was finished. By using the ANSYS software, a finite element model for the pre-stressed Stewart six-axis force/torque sensor was established. According to this model, the vibration modal was analyzed, and the natural frequencies and vibration modes were obtained. Finally, principle of the sensor calibration was analyzed, and the sensor coupling matrix was calculated according to the data of a static calibration experiment. Experimental results indicate that this pre-stressed Stewart six-axis force/torque sensor has the measuring ranges of 0～3 000 N for the force and 0～300 N·m for the torque, and its measuring accuracy is better than 7.5% of the actual data. It shows its advantages in wide measuring range, easy to decoupling and convenient for assembly.