Abstract: Phloem is an important part of vascular system and plays a key role in material transportation, signal transmission, mechanical support and defense reaction. Recently, studies on material transportation and signal transmission, especially the mechanism of loading and unloading of carbonhydrates, had made a great progress basing upon establishing a series of experimental system and methods. Several specific genes from phloem had been cloned. The molecalar mechanism of phloem loading had also preliminarily been demonstrated. The anthors reviewed some related results and raised some problems that should be solved in the future.