To achieve early diagnosis and online real-time monitoring of faults for a bearing, a new type of over constraint three-dimension force and moment sensor was put forward. By adopting six symmetrical distribution load branches which all did not pass their centers, the sensor could simultaneously measure the bearing radial load and axial moment. According to the static equilibrium equation, the mathematical model of measurement was established. Based on sensor measurement model and performance index, the performance of the sensor was analyzed, and the structure parameters were optimized. Then a sensor prototype and its load calibration experiment system were developed. Meanwhile, the load calibration experiment was carried out, and the measuring accuracy of the sensor was obtained.The calibration experiment shows that the radial force measuring accuracy is 2.56%, torque measurement accuracy is 0.92%, type I error is 2.56%, and the maximum of type Ⅱ error is 2.29%.The work lays a foundation for the applications of new constraint planar parallel three dimensional force/torque sensor to the online real-time measurements of bearings on radial loads and axial friction torques.