This present invention relates to a measuring device for measuring consistency of cement slurry for a consistometer. The measuring device comprises a high-pressure vessel, a slurry cup and a magnetic driver, wherein the slurry cup is rotatably mounted inside the high-pressure vessel by the magnetic driver, stir blades are hanged in the slurry cup, and the magnetic driver is driven by a driving motor which is located outside the high-pressure vessel and is further provided with a tension sensor. The invention cancels the conventional mode for measuring consistency by a potentiometer, uses the tension sensor to measure the torque transferred from the driving motor to the magnetic driver, i.e. the cutting torque created by the stir blades on cement slurries within the slurry cup, thereby measuring the consistency of cement slurry.