Aiming at the complicated working conditions of the cotton picker, a power shift stepless speed regulation driving transmission scheme with a combination of hydrostatic continuously variable transmission and mechanical step transmission was proposed. The control logics of three working modes of the cotton picker, such as field picking, field transportation and road transportation were established, and the speed ranges of the three modes were determined. The power transmission equation was construct, and the design parameters and hydraulic system components selection of the cotton picker were determined. A cotton picker prototype was built for field test, and the speed regulation characteristics and variable pump efficiency characteristics were analyzed. The results show that through the joint regulation of variable hydraulic pump, variable hydraulic motor and changing the transmission ratio of mechanical stepped gearbox, the constant torque output of the cotton picker in the field picking mode and the constant power output in the transportation mode can be realized; the field picking speed range of the cotton picker is 0~8.5 km/h, the field transportation speed range is 0~14.5 km/h, and the highway transportation speed is 0~27.5 km/h; the whole operation of the cotton picker can realize stepless speed regulation to meet the driving power demand of the cotton picker.