In order to make clear the regularity of tuberous root growth and amyloplast development in sweet potato,‘Xushu 22’ was used as the material in this study.The tuber growth and amyloplast development were studied by using resin semi-thin sections method.The experimental results showed that:(1)The primary growth of tuber with short duration time,the primary structure of tuber composed of epidermis,cortex and stele.The proportion of cortex on the cross section of tuber was bigger than that of stele.(2)The secondary growth of tuber started at 10 d after transplanting,the vascular cambium and the cork cambium formed in secondary growth.With the secondary growth,the parenchyma cells around the scattered vessel of secondary xylem dedifferentiated and formed accessory cambium by periclinal division.The vascular cambium,cork cambium and accessory cambium cooperated to make the tuber rapidly expanded.(3)The amyloplasts were first appeared in cortical cells as the secondary growth started,then appeared in large numbers in parenchyma cells which generated from secondary growth.The occurrence and development sequence of amyloplasts in tuber showed form outside to inside.(4)The starch granule in parenchyma cells had two types,the single starch granule and the compound starch granule.The parenchyma cells were mainly composed of compound starch granule in early stage of development,while parenchyma cells were mainly composed of single starch granule in later stage.The amyloplast with compound starch granule could divide and formed the amyloplast with single starch granule.(5)The starch could accumulate at whole period of tuber growth and the fastest accumulation rate appeared in middle period of tuber growth.