The main technical problem of potato mechanical partition harvest is the large workload for farmers to pick up, high labor intensity and low harvest efficiency. A potato combined harvester based on multistage separation technology was developed on the basis of planting patterns and agronomic requirements. It could implement digging, potatosoil separation, soil cleaning and potato gathering simutaneously under the condition of double ridge and double row. The harvester was worked by the tractor’s traction, the key parts of the harvester included depth control device of loosing soil, device of cutting soil and seedings, device of digging, shaking device of potatosoil separation, device of transition separation, device of removing soil and impurities and collecting device. The harvester adopted multistage separation technology, which could effectively improve the separation efficiency of potatosoil, reduce impurity content and labor intensity significantly. Field tests showed that loss rates were 1.64% and 1.59%, damage rates were 1.72% and 1.48%, and bruising rates were 2.31% and 1.92% and the productivity were 0.41hm2/h and 0.54hm2/h when the harvesting speeds were 3.17km/h and4.16km/h, respectively. All the performance indexes met the requirements of NY/T 648—2015 Technical Specification for Quality Evaluation of Potato Harvester. In addition, the dynamic impact information of potatoes was obtained during harvesting based on the impact detection technology. It was confirmed that the key position of the combined harvester to produce greater impact force was the junction of separation sieve Ⅰ and separation sieve Ⅱ and the end of collecting device. Reducing the height difference between separation sieve Ⅰ and separation sieve Ⅱ and improving the buffering effect at the end of collecting device were effective measures to reduce damage rate and bruising rate. It could provide a technical reference for further exploring the technology of potatosoil separation and the research of potato combined harvester.