Aiming at the poor separation effect and artificial pick up potato labor intensity of the one stage lift chain potato digger, the 4U-1600 set of pile type potato digger was designed. Based on the prototype designed and selected of key operation parts, and the structure and operation parameters of ladder digging blade, two stage lifting chain soil-potato separating and conveying device and hydraulic open type potato collecting box were determined. For further study of the improved working performance of set of pile type potato digger, the Box-Behnken experimental design with three factors and three levels was performed, parameters such as forward velocity, one stage soil-potato separating and conveying device velocity and two stage soil-potato separating and conveying device velocity were selected as independent variables, which would influence the potato obvious rate and potato injury rate. The mathematical model was established, and then the effects of various parameters and their interactions were analyzed as well. The test results showed that effects orders of three parameters on the potato obvious rate from primary to secondary were as follows: two stage soil-potato separating and conveying device velocity, forward velocity and one stage soil-potato separating and conveying device velocity. And effects orders of three parameters on the potato injury rate from primary to secondary were as follows: one stage soil-potato separating and conveying device velocity, two stage soil-potato separating and conveying device velocity and forward velocity. The optimal working parameters were forward velocity of 1.50m/s, one stage soil-potato separating and conveying device velocity of 1.37m/s and two stage soil-potato separating and conveying device velocity of 0.89m/s. Confirmatory tests showed that the average value of the potato obvious rate and the potato injury rate were 95.11% and 3.36%, which were up to the relevant work quality evaluation specification requirements, and the experimental results met the design requirements of potato digger.