Soil organic carbon (SOC) is an important component of soil organic matter and an important index to evaluate soil fertility. The purpose of this study was to investigate the effects of soil water saving and soil moisture conservation on surface soil structure stability and organic carbon sequestration capacity in rain-fed agricultural area of the Longdong dry tableland, Northwest China. In this study, the fine root growth of 0-20 cm topsoil of apple orchards with different plastic film mulching years (2,4,6 years) was investigated. The soil physical properties and texture was classified. With microbial biomass carbon (MBC), easily oxidized organic carbon (EOC) and particulate organic carbon (POC), soluble organic carbon (DOC), and other indicators, the dynamic change of characterization of soil organic carbon were evaluated. With the help of β-1, 4-wood glycosidase (βX), β-1, 4-glycosidase enzymes (βG), cellobiose hydrolysis (CBH) enzymes activities, the soil carbon metabolism circulation features were characterized. The relationship between root growth, soil physical structure, soil carbon metabolism enzymes activities and organic carbon sequestration under different plastic film mulching years were established to investigate the response of surface soil organic carbon to physical "recessive" degradation. The results showed that:short-term film mulching (2Y) effectively improved soil water content, total porosity, capillary porosity, reduce soil bulk density, which was 112.39%, 105.65%, 104.29%, 90.08% of CK. As a result, the growth of fine roots and the active organic carbon contents were promoted. The contents of POC, DOC, MBC and EOC were 220.11%, 129.42%, 151.35% and 111.72% of those of CK, resulting in the increased total organic carbon of 137.21% compared with that of CK. Long-term film mulching (6Y) showed a "recessive" degradation of surface soil, and the deterioration of soil pore structure was dominated the growth of fine roots. The EOC and MC were decreased significantly by 46.88% and 43.54%, compared with the CK. βX, βG and CBH enzyme activities, as the dominant factors determine the variability of organic carbon storage, accounted for only 65.60%, 53.08%, 47.04% of CK. The damage of surface soil structure under long-term plastic mulching conditions led to the inhibition of root growth, which resulted in the decrease of soil carbon metabolism enzyme activity, carbon pool management index and organic carbon storage, which was not conducive to the long-term, stable and healthy development of soil quality. Short-term film mulching for 2 years was suitable for apple cultivation in the Longdong dry tableland. In order to provide theoretical basis for improving the adjustment vnechunism of soil physical structure evolution, soil fertility improvement, root grouth and drought-resistant cultivation technology of fruit trees in rainfed agricultual areas of the Loess Plateau.