Abstract: Carbon assimilation accumulation and partitioning was studied in one-year-old fruiting limbs of greenhouse-grown "Ruiguang 5" nectarine (Prunus persica L. var. nectarina Ait), affected by about 10%～12% shading treatment (simulating the light intensity decrease due to dust accumulation on greenhouse covering by adding old plastic film to it) during the second rapid swell of peach fruit growth. The results showed that net photosynthesis rate and starch content decreased markedly and total soluble sugar content changed little in leaves of terminal shoot under shading conditions. After labeling terminal shoot by ¹⁴CO₂, more carbon was found to export from fed shoot to the nearby fruit and less carbon to the distant fruits. Moreover, a reduction of carbon assimilation partitioning in mesocarp was also observed within fruit. Fruits harvested in fruiting limbs by shading treatment were observed to have less fresh weight and transverse diameter and poor red coloration. Therefore, to improve the fruit quality it is necessary to increase the sunlight intensity inside greenhouse as far as possible during the second rapid swell of peach fruit growth.