Abstract: A field experiment was conducted to determine the effects of organic fertilization on arid soil nutrients of winter wheat under different organic fertilizer applications, and to provide guidelines for establishing the soil amelioration technical system for the Weibei tablelands of Shaanxi. There were 3 manure application amounts （MH: 22 500 kg/ha, MM: 11 250 kg/ha and ML: 5 250kg/ha), 3 wheat straw returning amounts（SH: 9 000 kg/ha, SM: 6 000 kg/ha and SL: 3 000kg/ha）treatments, and taking no organic fertilization as the control. The soil nutrients, soil labile organic carbon (LOC) and enzyme activities are analyzed for four years (20072010). After the wheat harvested in 2010, the results of the four years field experiment show that different organic fertilization amounts have different effects on the contents of soil available nutrient and labile organic carbon in 060 cm soil layer, the order is: MM, SM＞SH, MH＞ML, SL＞CK. Compared with the CK, the contents of soil available P, available K, alkaline hydrolytic N and LOC are increased by 13.27%161.77%, 7.51%25.01% (P0.05), 10.52%41.87% (P0.05) and 64.15%92.42% (P0.05), and there are no significant differences between the two kinds of fertility fertilization. The activities of urease, phosphatase and invertase in 060 cm soil layer are significant increased（P0.05）, and the SM and MM treatments have the most significant effects, while the catalase activity is not changed significantly. This study shows that in semi-arid areas the straw returning and organic fertilizer application can play an active role in improving soil LOC, promoting soil nutrient availabilities and enzyme activities significantly.