The invention discloses a high-power tractor hydraulic machinery stepless speed changer adopting a novel structure design scheme. The high-power tractor hydraulic machinery stepless speed changer is characterized in that a power input shaft (3) and a power output shaft (9) are always positioned on the same axial line, when a high-power tractor runs or parks, the PTO (power take off) output can be realized through the action of an independent operation double-action clutch (2), and the output power of four sections is respectively the power output after busbar hydraulic power and mechanical power are converged by a front planetary row (16) and a back planetary row (15). The speed changer has the following characteristics that the structure is compact, the dimension is reasonable, the power distribution can meet different work conditions of the tractor, in addition, the output rotating speed and the output torque can be automatically regulated according to external load changes, and an engine is enabled to work in the optimal state. The design scheme has the advantages that the advantages of mechanical step speed change and static hydraulic stepless speed change are integrated, the power of the four sections is respectively output after hydraulic machinery confluence, and the transmission efficiency is improved.