Abstract: In order to reduce damage rate and loss rate in process of Cyperus esculentus harvesting and improve screening rate, a compound screening Cyperus esculentus harvester composed of lifting net chain, threshing drum, key separation device, impurity blower, horizontal chain conveyor and impurity suction fan was designed．For key separation device, key component of the machine, orthogonal test was carried out with crankshaft speed, separation device angle and baffle angle as factors, and screening rate and falling particle loss rate as indicators．Regression equation and response surface model were established by using Design-Expert software．Harvest efficiency and loss rate of leaking beans of prototype were tested through field experiments．