Abstract: Now the separation of sweet-potato-stalk separator of sweet potato combine is incomplete in China, the number of sweet potato damage is large, blockage of soil block and components of stalk entanglement are urgently solved. This paper designed the sweet-potato-stalk separator of simple, high-extraction rate, low-damage rate and anti-soil blockage. It mainly consisted of excavation and conveying parts, transmission parts, picking roll and conveyor bar lifting chain. According to design calculation and growth characteristics of sweet potato, main structure-parameters of separator were determined, in which length of excavating part was 382 mm; length of conveying device was 1 668 mm, horizontal inclination of conveying device was 24°; radius of driving shaft and picking roll was 18 and 36 mm respectively; distance between lower layer bar and picking roll was 27 mm, and distance between uppermost end and picking roll was 251 mm. In terms of operation process of sweet-potato-stalk separator, sweet potato mixture was thrown from highest point of conveying device at a determinate inception speed into picking roll. For convenience of theoretical analysis, sweet potato mixture regarded as a particle, regardless of interaction between mixtures. Motor process could be regarded as oblique projectile motion. Analysis of movement characteristics of sweet potato, ascertaining main work-parameters of sweet-potato-stalk separator was moving speed of machine, rotation speed of driving shaft and angel of between delivery device and horizontal. Through experiment of sweet-potato-stalk separation, it found that moisture content of sweet-potato-stalk decreases all time during harvest period, while changing of separating force increased first, then decreased, and finally flattened out, and mathematical model of relationship between moisture content of sweet-potato-stalk and separating force conformed to quadratic function. With Box-BenhnKen, central combination design method selected effects of 3 main work-parameters on extraction rate and damage rate of sweet potato and conducted experimental design. Based on this, one-time three-factor and three-level regression orthogonal experiment carried out. Experimental sweet potato planting mode single ridge single row, soil clay, and soil moisture content 22.8%. Since self-propelled sweet potato combine harvester contained three-stage soil potato separation device and forward system was crawler chass, test ground could be very good to meet harvest requirements. In accordance with test results, regression analysis of extraction rate and damage rate of sweet potato in DESIGN EXPERT was carried out, and significant level of each factor was determined. According to contribution rate of factors, 3 parameters were identified for primary and secondary order of influence of extraction rate and damage rate. The result was angel between delivery device and horizontal>moving speed of machine>rotation speed of driving shaft. Response surface method used to establish quadratic polynomial mathematical model of influence of parameters. The optimal combination of field trial parameters was that moving speed of machine was 1.20 m/s, rotation speed of driving shaft was 895 r/min, and angle between delivery device and horizontal was 24°. Extraction rate and damage rate of optimal parameter combination field test results were 98.14% and 2.76%, respectively, and separation effect satisfied sweet potato harvest requirement. The study also provides ideas for other fruit-seed separation operations.