Abstract: The paper aims to study the cause of frost damage of young loquat fruit in temperature range from -3℃ to 0℃. After rain and snow weather, fruits showed freeze injury and those without injury by treatments of bagging and covering with plastic film were collected to check the freezing condition and detect the content of free proline and other physiochemical indexes. The results showed that: fruits covered with plastic film were protected from cold, and fruits without plastic film protection were exposed to rain and snow showed freeze injury; in the treatment of bagging, the fruit parts without contacting the bag were not injured, while the parts close to the bag showed freeze injury; the content of free proline in fruits with freeze injury was significantly higher than that of fruits without injury; the MDA content in bagging fruits with freeze injury was significantly higher than that of bagging fruits without injury, while the MDA content showed no significant difference between fruits with or without plastic film covering; the activities of SOD, POD and PPO all showed significant differences between fruits with or without plastic film covering, and they were all higher in fruits without covering; however, their activities were all very low in bagging fruits, and showed no significant difference between the freeze injured bagging fruits and no injured fruits. The results suggest that in the temperature range from -3 to 0℃, the low temperature conductive medium of different forms (air, liquid and solid) may be the main cause of freeze injury in young loquat fruit, and the liquid and solid conductive medium will lead to freeze injury. The content of free proline in loquat fruit may be the key index to identify whether the fruit is freeze injured.