Abstract: In order to reduce the sugar loss of sweet sorghum stalk during natural storage and to understand relation between sugar loss and change of enzyme activity, the effects of pretreatment of sweet sorghum stalk with plant growth regulator including gibberellin (GA3), potassium salt of maleic hydrazide (KMH), and Na salt of naphthalene acetic acid (NAA-Na) on its sugar content and change of related enzyme activity during natural storage were investigated. Results showed that the storage period of sweet sorghum stalk can be prolonged to 3-4 months with pretreatment of suitable types and doses of plant growth regulators. The sugar contents of sweet sorghum stalks with pretreatment of GA3 (40 mg/L), KMH (400 mg/L) and NAA-Na (70 mg/L) after 112 d storage were 95%, 92% and 94% of their initial sugar contents, respectively, which were significantly higher than that of the control . In addition, the pretreatments of sweet sorghum stalk with suitable types and doses of plant growth regulators can significantly regulate its biological enzyme activities related to aging and sugar metabolism. Three types of plant growth regulators can slow down the sugar loss of sweet sorghum stalk after harvesting through regulating related enzyme activities. The research can provide a scientific reference for the storage of sweet sorghum stalk for large scale bioethanol production.