Abstract: By the randomized block design,effects of using plastic sheets for mulching on the yield and quality of the summer sweet potatoes,Longshu 24,were studied.The results showed that the plastic sheet-mulching increased the yield significantly.The average fresh tuber yield was 55.13t.hm-2 from the two years experiment.It was higher than that of CK by 22.9%.The average yield of the sweet potato dry matters,from the two years experiment,was 15.92t.hm-2.It was higher than that of CK by 20.0%.The differences were significant.The dry matter content of the sweet potatoes was lower than that of CK by 0.7%,and the starch content was lower by 0.61%.There was no significant difference on the overall root quality during the harvest period.The reasons that the plastic sheet-mulching could promoted the sweet potato yield were believed to include:(a)the weight pre plant of the tuberous roots was increased significantly;(b)the T/R radio during early and mid growing stages was reduced,while the root development during the peak stage was enhanced with the mulching;(c)the soil′s volume weigh was decreased,porosity dicreased,permeability improved,and water content remained relatively stable which rendered the soil conditions conducive to the plant′s development;(d)the plastic sheet-mulching improved the soil ecological environment that benefited the root growth and development;and(e)the mulching encouraged the root thickening resulting in improved the plant′s nutrient and water absorption.The increased efficiency by the application of plastic sheet-mulching was found to be most significant,that is,every hectare could increase a net income of 13000 yuan.