This invention discloses a method and apparatus for measuring the weight of a CNC workpiece. As the weight of the workpiece on a loading platform increases, the loading of a driving module which drives the loading platform in constant speed increases accordingly. On the contrary, as the weight of the workpiece on the loading platform decreases, the loading of the driving module which drives the loading platform in constant speed also decreases. This invention determines the weight of the workpiece on the loading platform by measuring the electrical signal which drives the driving module and utilizing a calibration curve data in a preconfigured database.