Gannan navel orange was used to study the effects of self-developed magnesium fertilizer containing trace-elements （MG1）， calcium-magnesium fertilizer containing trace-elements （MG2）， instant magnesium fertilizer in soil spraying （MG3S）and foliar spraying （MG3F）on quality and nutrients of fruit to solve the declines in yield and quality of fruit in Gannan navel orange caused by exchangeable magnesium and trace-elements in the soil of citrus orchards in China. The results showed that the application of four types of magnesium fertilizers significantly increased the yield of fruit， with an increase of 28.82% and 24.76% in MG1 and MG2， and 18.78% and 16.01% in MG3S and MG3F， respectively. The application of magnesium fertilizer significantly increased the quality of single fruit， the content of soluble solids and vitamin C， the ratio of solids to acid， and improved the quality of fruit. Among them， the comprehensive score in MG2 was the highest， indicating the quality of fruit is the best. Magnesium fertilizer containing trace-elements significantly increased the accumulation of nutrients in fruits. The calcium carrying capacity and the magnesium carrying capacity of MG1 and MG2 increased by 32.12% and 53.50%， 25.28% and 29.90%， respectively. The accumulation of nutrients including nitrogen， boron， zinc， and molybdenum in fruits increased significantly as well. It is indicated that the application of magnesium fertilizer has a significant effect on increasing the yield and improving the quality of Gannan navel oranges. Magnesium fertilizer and calcium magnesium fertilizer containing trace-elements can significantly improve the content of nutrients including calcium， magnesium， boron， zinc， and molybdenum in the tree， with the best effect on increasing the yield and improving the quality. The application of instant magnesium fertilizer in soil spraying and foliar spraying have similar effects.