Storm cells are the basic units that form various types of severe convective weather. Their radar echoes have complex shapes，uneven internal distribution，and intertwined outer layers，which makes cell segmentation difficult. This paper proposes an automatic iterative segmentation method for convective cells based on their morphological structure characteristics. Taking the cell segmentation results based on the region-tree structure on the radar image as the initial input，in each iterative segmentation process，the three morphological structure features of each segmentation result are first calculated，and then a pre-trained SVM classifier is used to determine whether the segmentation result is a convective cell. The segmentation results that are not cells are segmented again. The method in this paper was tested through three storm cases with different types. The results show that the method can effectively identify aggregated cells and cells in a split/merged state，and can obtain the complete structure of cells. In the quantitative evaluation test，the algorithm presented in this paper obtained a Critical Success Index score of 0.84，which is higher than that of the traditional SCIT method （0.55） and the single threshold method （0.49）.