The present invention provides a Suspended Wheel Reducer and a suspended wheel crossing-zero multilevel transmission, both of which comprise a front planetary gear train, a rear planetary gear train and a suspended wheel. With different design for the dimension of the gear wheels contained in the front planetary gear train, the rear planetary gear train and the suspended wheel, it's possible to achieve optional different reduction ratios. The Suspended Wheel Reducer and the suspended wheel crossing-zero multilevel transmission have simple configuration, higher reliability, thus overcoming the drawback in prior art, in which a transmission mechanism for multilevel gear shift mechanism is required to achieve greater reduction ratio, reducing its overall dimensions and cost.