Abstract: In China, nitrogen fertilizer is excessively used in sugarcane planting areas, and nitrogen use efficiency（NUE）of sugarcane varieties is low. Breeding of high NUE varieties is an effective way to improve the NUE and reduce nitrogen fertilizer application. Mining key miRNAs in response to nitrogen deficiency stress and studies of their biological functions in sugarcane are the theoretical basis for the development of sugarcane varieties with high NUE. The research team found that ScmiR393 is an important regulatory factor in sugarcane response to nitrogen deficiency stress. To further investigate the biological functions of sugarcane ScmiR393 under nitrogen deficiency stress, the ScmiR393 gene was transferred into rice to obtain the homozygous ScmiR393-overexpressed transgenic rice. This study investigated the changes in the agronomic traits, photosynthetic characteristics, and the activities of nitrogen metabolism key enzymes in the ScmiR393-overexpressed transgenic rice under nitrogen-deficient conditions. The results revealed that under nitrogen deficiency stress, compared with wild-type rice, the activity of glutamate dehydrogenase in the roots of transgenic rice were significantly decreased, the activity of glutamine synthetase in the stems were significantly decreased, and the chlorophyll relative content and maximum photochemical efficiency of the flag leaves were markedly reduced, leading to inhibit photosynthesis. While the number of tillers was significantly increased, the increase in plant root number, root surface area, and root volume was significantly decreased in transgenic rice. In summary, ectopic expression of sugarcane ScmiR393 has the potential to reduce the capacity of nitrogen assimilation, reduce the efficiency of photosynthesis in flag leaves, and inhibit plant growth. In the research, the mechanism of nitrogen deficiency tolerance in the ScmiR393-overexpressed transgenic rice was studied, and the biological function of ScmiR393 under nitrogen deficiency stress was explored, which provided the theoretical basis and key gene elements for nitrogen efficient breeding in sugarcane.