It is the main trend of the mechanical oil recovery development that the sucker rod pumping unit with long stroke and large load, the conventional beam pumping unit don't adapt to the requirement. The double crank-pulley extending-range pumping unit was designed on the research basis of the tower steel wire rope non-beam pumping units, motor output movement was retarded by roller chain drive and three-ring gear reducer, the double crank connecting rod drove the weight box and range-drums to move up and down, and thus the pumping movement was achieved. The pumping unit has its own advanced features, such as good energy-saving effect, high reliability, smooth operation and convenient maintenance. It has good application prospects.