According to the magnesium status of soil in South China, the fertilizer effect of magnesium fertilizer on more than 20 crops was studied, and rich production data were obtained. The test results showed that the yield of tobacco, sugarcane, rape, soybean, sweet potato, pepper, tomato, citrus, pineapple and banana increased by 285.0, 8850.0, 105.0, 120.0, 1035.0, 4485.0, 5655.0, 3705.0, 300.0 and 1665.0kg per hectare respectively. The results showed that the application of magnesium fertilizer could prevent and control the yellow leaf rate of rice and reduce the yellow leaf rate by 20.2%, and the effect of base fertilizer was the best. The application of magnesium fertilizer made the rice green faster and divide early, increased the number of effective panicles, the number of grains per panicle and 1000 grain weight, and thus increased the yield. The application of magnesium fertilizer increased the average yield by 522.0kg/ha compared with the control. In addition, the Nanjing Institute of Soil Sciences of the Chinese Academy of Sciences has also conducted a large number of experiments on potassium magnesium sulfate and magnesium alum, mainly in Guangdong, Guangxi, Jiangxi, Hunan and Yunnan. The crops involved include grain crops, oil crops, cash crops, vegetables and fruits. The results show that the performance effects of different crops are different, and even the same crop has a certain range of yield increase, However, the general trend is that magnesium fertilizer has different yield increasing effects.