Abstract: In order to explain the genesis and development of the digestive system,we studied the embryonic development of the swimming crab,Portunus trituberculatus,by histological section.The results showed that the foregut,mid-gut and hind gut arised in the gastrulating stage.The foregut differentiated an esophagus and a stomach in the egg zoea Ⅰ.The stomach opened to the yolk sac.The hind gut epithelial cell did not arrange in order during the egg naupliusⅠand Ⅱ.The epithelial cell formed hind gut cavity in the egg zoea Ⅰ.The hind gut touched with the midgut in the egg zoea Ⅱ.The mid-gut developed to a cup-like structure in the egg zoea Ⅱ.The digestive system formed when the mid-gut touched with foregut before hatching.