Coolant temperature controlled foam box is widely used in fresh fruits and vegetables package. However, it is found that the increase of the amount of coolant can't improve the quality of fresh fruits and vegetables. The mechanism of the problem was studied. The tip of the lettuce was packed in a foam box with different amount of coolant (100, 400, 800 g) which simulated normal temperature (25 ℃) logistics transport process. The results showed that in the early and middle logistics process, each treatment group could maintain low weight loss rate, good color and nutritional quality (chlorophyll content, vitamin C content); but at the end of the logistics process, the respiration of lettuce consumed O2 and produced CO2 which caused gas damage and decay eventually. Coolant controlled temperature foam box has obvious stage effect on the preservation of lettuce; it can be divided into three stages: low temperature-high humidity, modified atmosphere and gas injury. Increasing the amount of coolant used in the insulating package is beneficial to maintain the quality of lettuce tip at the early stage of the logistics process, but the effect of prolonging the shelf life is limited. The main factor that restricted the preservation effect of the coolant controlled temperature foam box is the anaerobic respiration caused by the change of gas composition in the box.