The whole design adopts the stepless variable speed AC motor series transmission with step speed regulation. The speed switch of the transmission adopts the shift fork to move the two sets of double gears of the input shaft to change the transmission ratio, so that the main shaft can output 16 step speed within the speed range. The operating mechanism uses double hydraulic cylinder to drive the fork to operate the double gear, so that the input shaft gear can switch the engagement point.At the same time, it improves the overall transmission efficiency and the overall design meets the requirements of automation.