The utility model discloses a device of flyer speed is measured with law of conservation of angular mo mentum, a serial communication port, including bottom plate, support, pendulum rod, axle, driving lever, calibrated scale, pointer, check ring, flyer and arithmetic element, the gasket -mounted is on the workstation, support and bottom plate fixed connection, pendulum rod and axle fixed connection, the axle is installed in the axle mounting hole, and can wind the support free rotation, the support top have with an axle mounting hole coaxial arc driving lever groove, the calibrated scale is fixed on the support with the axle center with the axle mounting hole, the pointer is pressed close to the calibrated scale and is fixed epaxial, the check ring is fixed the outer the tip of the axis of pointer, the flyer is strong magnetic material, the flyer with the collision of pendulum rod is two collisions between the rigid body, the arithmetic element calculates according to law of conservation of angular mo mentum the speed of flyer. The utility model discloses simple structure, convenient and fast, low cost.