In the teaching of rigid body rotation, we first explain the moment of inertia of regular rigid bodyand then guide students to deduce the moment of inertia of cuboid rigid body. Then we propose how to measurethe moment of inertia of smart phones. We guide students to measure the moment of inertia of mobile phones byusing gyroscope sensor and phyphox software of smart phones , and get good results. 0n the one hand ,there is noneed for complex and huge demonstration instruments.Teachers and students can directly operate and measurein class. and students can also make measurement and calculation as homework alter class.0n the other handthis demonstration experiment integrates several knowledge points of rigid body motion,such as the calculationof moment of inertia of regular cuboid, the law of parallel axis and the rotation of rigid body. The above workprovides a beneficial attempt for the integration of smart phones into college physics demonstration teaching.