Abstract: The effects of potassium on sucrose and glucose content, sugar metabolism related enzyme activity and the expression of related genes in maize root infected with Fusarium graminearum were studied under sand-culture experiment. The results showed that under K stress, pathogen infection led to significant decrease of sucrose and glucose contents. The sucrose content declined more quickly than that of glucose. With the process of infection, the ratio of glucose to sucrose increased in no potassium applied treatment; 8 days after infection, the ratio was 10 times higher in K deficient roots than in K adequate roots. Besides, after inoculation, the activity of sucrose phosphate synthase (SPS) and sucrose synthase (SS) were increased as well as the gene expression of sps and ss in potassium treated maize root. In K-treatment, sps gene expression increased in 6 days after inoculation, and no change of ss expression was observed in K-stressed root. This study demonstrated that K could enhance maize resistance to stalk rot by regulating sugar metabolism related enzyme, consequently, maintain the optimal sugar metabolism in infected position, and enhance the resistance to stalk rot.