The invention provides a stepless speed changer, which can prolong service life of engine and drive system, and has simple structure, operation and control convenience, low cost and high energy-saving efficiency. And the key points of its technical solution: it comprises input shaft, controllable moment apparatus, empty reverse gear mechanism, clutch, and output shaft, where there are several moment increasing units composed of planetary gear sets connected in turn, where each moment increasing unit comprises input component, output component, common output component, and planetary gear, the input component of the first moment increasing unit is connected with the input shaft and the common output component is connected to the output end of the controllable moment apparatus and then connected to the input end of the empty reverse gear mechanism, and the output unit of the last moment increasing unit is connected with the input end of the controllable moment apparatus.