In order to improve the work quality of carrot harvester, roots and stems cutting device of carrot was designed based on statistical analysis of physical parameters of carrot. This device consists of leveler, gripping delivery mechanism, double disc blade cutting device and upper gripping delivery mechanism. Force analysis of double disc blade cutting device was done by the means of graphic analysis, the request of stems being cut was obtained by the experiment; rotate speed of disc blade was determined at 312~325r/min by analyzing the operation velocity. The working parameters of disc blade were calculated according to the agricultural requirements and the objective of low energy consumption. Two kinds of blades were designed, and cutting rate and root damage rate were chosen as the experiment indicators. The contrast test was done and the result showed that operation performance of the ordinary disc blade and blade with serrated edge was approximate. Both of above blade’s cutting rates were more than 90%, and the root damage rate was less than 2%. Taking the economy into consideration, field experiment was done with the ordinary blade, the result showed that when the device worked at the speed of 1.34m/s, the net rate was 98.3%, cutting rate was 90.6%, root damage rate was 1.8% and the total losing rate was 3.5% which met the requirement of carrot harvester.