The invention discloses a method for monitoring the running state of a high-speed train gear box and belongs to the field of state monitoring of gear boxes. The method includes the following steps that vibration acceleration sensors are arranged in the X direction, the Y direction and the Z direction of the gear box and used for acquiring vibration acceleration signals in all direction of the gearbox; wavelet energy of the vibration acceleration signals on each frequency band serves as characteristic parameters of the running state of the gear box; according to historical data generated when the gear box runs normally, a characteristic parameter sample training database is generated; classical field matter-element models and joint field matter-element models in all the vibration directions are built when the gearbox runs normally; classical fields of characteristic parameters of the matter-element models in all the vibration directions are optimized and determined, a matter-element model of the current running state of the gearbox is built, the comprehensive correlation degree between the current running state and a normal running state is calculated, and whether the current gearbox normally runs or not is judged. The method for quantitatively and qualitatively judging the running state of the gear box is provided, and a basis is provided for monitoring the state of the gearbox.