The invention discloses a three-shaft tourbillon mechanism of a mechanical watch. The three-shaft tourbillon mechanism of the mechanical watch comprises a tourbillon, an outer shaft frame and a differential mechanism which are fixed to a driving wheel. The driving wheel is meshed with a power input wheel, the rotary shaft axis of the tourbillon is vertical to that of the outer shaft frame, an idle wheel is meshed with a second gear shaft fixed to an inner shaft tourbillon, and the differential mechanism comprises a third shaft planetary mechanism of a lower supporting mode. The three-shaft tourbillon mechanism of the mechanical watch has the advantages that due to the fact that the planetary mechanism in which the lower supporting mode is adopted serves as a third rotary shaft, manufacturability of the overall structure is high, especially a cylindrical roller bearing is easy to machine, machining cost of parts is low, and the three-shaft tourbillon mechanism is suitable for industrial production in bulk; the motion trail of the three-shaft tourbillon is updated to be of a sphere shape from a column shape, an internal regulating mechanism moves three-dimensionally at multiple angles, the motion trail of the internal regulating mechanism is more complicated, an effect on offsetting earth gravity is more obvious, and the mechanical watch runs more accurately.