Abstract: Natural biology has evolved over millions of years and has formed near-perfect structure. Study on the structure of natural biomaterials is the basis of bionic research. The microstructural features of the shell of Hyriopsis cumingii, including the stratum corneum, prismatic layer, nacre, the interface between them and the topographys of trip-like crystal ribbon were described by using the SEM and AFM. The shape and size of the aragonite platelets and the dimensional change between the layers were measured according to the observations. The results show that there exist cracks in the stratum corneum. There is no obvious transition interface between the nacre and the prismatic layer. The structural defects of strip-like crystal ribbon are found in the nacre. The thickness of the whole shell and nacre increases first increases and then decreases along the 0 growth line, while the thickness of the monolayer aragonite tablet is uneven. The thickest part of the platelet can be more than twice as the thinnest part. The structure of the Hyriopsis cumingii was studied further, which provides a theoretical basis for its excellent mechanical properties, and provides new directions for the future bionic structure design.