PASCO rotary motion sensor can accurately measure and record the angular velocity of the objectwhen it rotates in real time.ln the experiment of measuring moment of inertia of rigid body by the falling bodymethod ,in order to improve the accuracy of the experiment , the PASCO rotary motion sensor is used to directlmeasure the angular velocity and calculate the angular acceleration.The improved instrument simplifies theexperimental steps and improves the experimental accuracy. The relative errors of the three groups ofexperiments are 0.2%,0.7% and 0.3% respectively.The experimental results are accurate.  According to theexperimental results,the improved instrument is easy to operate and has higher measurement accuracy.