According to the problems of field plastic film pollution caused by the cultivation pattern of potato big ridge double line which was promoted in large area in Northwest China, the combined operation machine for potato harvesting and plastic film pneumatic auxiliary collecting was designed, which had synchronous implementation function of potato harvesting and plastic film pneumatic collecting. Based on design and selection of key operation parts for the prototype, the structure and operation parameters of ladder digging blade, soil-potato dither conveyor device and floating pneumatic curl-up film mechanism were determined. The operation process of floating pneumatic curl-up film mechanism was analyzed and the conditions to make sure that the floating pneumatic curl-up film mechanism did not produce the phenomenon of plastic film remained and jam, tensile and skid were achieved, the conditions of wheel did not slip but rolling in the field were analyzed and calculated. For the relevant work performance test of prototype, the field experiment results showed that when the operation speed of the combined operation machine was 1.8~2.0km/h, the plastic film collecting ratio was 91.6%, the obvious ratio of potato was 96.8% and the injury ratio of potato was 2.3%, which met the relevant work quality evaluation specification requirements, and also the experiment results met the design requirements of combined operation machine. The research achievement would provide an important reference for root-tuber crop collecting machine development under plastic film mulching cultivation.