Granulation is a physiological disorder of citrus fruits,which causes juice sac crystallization,reduction of juice,loss of sugar and organic acid,and seriously affects the edible and commercial value of citrus fruits. In this article,the physiological and molecular mechanism in the granulation of citrus fruit is expounded from aspects of cytology,quality and nutrition of fruit,hormone levels,activities of enzymes and molecular biology. It will lay a foundation for further studying the mechanism and control measures in the granulation of citrus fruit.