Abstract: Gibberellin synthesis genes play an important role in plant growth and development. The super dwarf mutant ai-gan1 (ag1) induced by ethyl methane sulfonate (EMS) showed obvious defects in internode and leaf elongation. The plant height at mature stage reached only 34.81% of the wild-type (WT) height. The panicle length and the ratio of internode length to the whole plant height changed significantly. The proportion of the last second and third internodes had a significant decrease in the total length. Mapping-by-sequencing (MBS) and CRISPR-Cas9 mediated gene knockout confirmed that the mutant gene was an allele encoding gibberellin 3-beta-hydroxylase 2 (GA3ox2). Morphological analysis showed that the length of inter-node cells in the penultimate internode of the mutants was significantly shorter, and the number of longitudinal cells was significantly reduced. The number of transverse parenchyma cells in internodes increased significantly, and the number of transverse venules in flag leaves of the mutants increased significantly, but the number of longitudinal parenchyma cells around vascular bundles decreased significantly. At the same time, the expression levels of some genes related to cell division and elongation were significantly decreased in the mutants. The results showed that GA3ox2 in rice seriously affected the elongation of aboveground internode cells and the cell division activity in internodes and flag leaves, which led to the abnormal morpho-logy of the aboveground part of rice.