The field experiments were conducted to delay the harvest cultivation of ponkan (Citrus reticulata Blanco cv.ponkan) in 2007 and 2008 using low-cost protected cultivation (plastic-film greenhouses and solar-shading nets) combined with ground plastic-film mulching.To evaluate the effect of protected cultivation on the improvement of fruit quality,the content of total soluble solid,titratable acidity,sugars and acids in ponkan fruits were measured under different cultivation models.Results showed that total soluble solid and titratable acidity of fruits from low-cost protected cultivation were higher than that of untreated control,while the volume of puffiness rate was significantly lower than that of the control.There was no significant difference in total soluble solid and titratable acidity between plastic-film greenhouses cultivation and solar-shading nets protected cultivation in the late development season of fruit.The sucrose,glucose and fructose content of all treatments increased with fruit maturity,whereas those of the control decreased in delayed harvest.Total sugars of fruits from ground plastic-film mulching in plastic greenhouses and plastic-film mulching under solar-shading nets were significantly higher than that of the control in the open field with delayed harvest,and there was no significant difference between two protective cultivations.The citric acid content during fruit maturation under different treatments shared a similar change,and the content of fruits from plastic-film mulching was higher than that of control in delayed harvest.