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For further integration agronomic requirement of planting technique of tiny ridges surface with whole film covering in dry land, in order to meet the requirements of mechanical high performance construction seedbed of whole plastic-film mulching on tiny ridges, a combined operation machine was designed, which synchronously realized institutional operation once such as ridging, filming and covering soil on tiny ridges. Based on the prototype, the important working parts such as the driving system, covering soil system and ridge shapingpressing device were designed. According to the requirements of related operation performance, the key working parameters such as the amount of soil covered on plastic-film mulching seedbed and the velocity of scraper type soil lifting device were analyzed, and the composition of test factors and their value range were determined. Response surface analysis was applied to optimize working parameters of the operation machine. Parameters such as the operation machine speed, the velocity of scraper type soil lifting device and the inclination angle of covering device were selected as independent variables, which would influence qualified rate of seedbed construction. The mathematical model was established, and then the effects of various parameters and their interactions were analyzed as well. The effects order of three parameters on qualified rate of seedbed construction was obtained. The optimal working parameters of operation machine were operation machine speed of 0.71m/s,the velocity of scraper type soil lifting device of 0.50m/s and the inclination angle of covering device of 68°. Confirmatory tests showed that the average value of qualified rate of seedbed construction was 95.6%, compared with before the optimization it was promoted significantly. Application of discrete element method to simulate the dynamic operation process of elevating, conveying and covering soil under the condition of optimal parameters of operation machine. The simulation result was consistent with the field test conditions, which showed that the machine optimization operation parameters calculation was accurate and reliable.