Precooling is one of the key measurements for litchi fruit preservation after being harvested, and the performance of precooling has a great influence on the quality change of litchi fruit. In order to investigate the heat and mass transfer during the precooling process, a mathematical model was built to describe the heat and mass transfer phenomenon in the test bed with controlled atmosphere for fruits and vegetables. The mathematical model was built based on the theory in heat dynamic mass transfer, and the temperature and moisture loss of the litchi fruit during precooling process was calculated. The effects of fruit weight and initial temperature on the process were investigated. After that, some results can be made. The time of precooling became longer as the weight of fruit was increased, however, the speed of moisture loss would be decreased. When there were 10kg litchi fruits, it took about 350min for the temperature of fruit decrease from 25℃to 5℃ by the same stack method, and the weight loss rate was roughly 2.16% after precooling. It can also be drawn that the speed of weight loss can be reduced by decreasing the initial temperature of litchi fruit. A test was done to verify the accuracy of the model, and the test results were matched well with the results from calculation, the maximum difference between them in fruit temperature and weight loss rate was 2.8K and 0.3%, and the mean difference rate was 13.1% and 10.7%, respectively. The research results can be useful for the investigation of the heat and mass transfer mechanism in a cool room and can be used to predict the temperature and weight loss of fruits during precooling process.