Abstract: The nitrogen application rate in sugarcane area of China was relatively high, and the nitrogen utilization efficiency of sugarcane varieties was relatively low. The cultivation of nitrogen-efficient sugarcane varieties was an effective way to improve the nitrogen utilization efficiency and reduce the nitrogen application rate of sugarcane. Exploring the key miRNAs of sugarcane in response to nitrogen deficiency stress and studying their biological functions were the theoretical basis for the molecular breeding of sugarcane varieties with high nitrogen use efficiency. ScmiR393 was previously found to be an important regulatory factor for sugarcane in response to the nitrogen deficiency stress by the research team. In order to further explore the biological function of sugarcane ScmiR393 under the nitrogen deficiency stress, ScmiR393 of sugarcane was transferred into rice to obtain a homozygous ScmiR393-overexpressed transgenic rice line. The changes of agronomic traits, photosynthetic characteristics and the key enzyme activities of nitrogen metabolism in the ScmiR393 -overexpressed transgenic rice before and after the nitrogen deficiency stress were studied with the wild-type rice as the control group. The results showed that after 10 days of nitrogen deficiency stress, the activity of glutamate dehydrogenase in the roots of ScmiR393 -overexpressed transgenic rice was significantly lower than that of the wild-type rice, and the activity of glutamine synthetase in the stems was significantly lower than that of the wild-type rice. The relative chlorophyll content and maximum photochemical efficiency in the flag leaves decreased significantly, thus the photosynthesis was inhibited. The number of tillers increased significantly, and the increase of root number, root surface area and root volume decreased significantly. In summary, Sugarcane ScmiR393 may have the ability to reduce the nitrogen assimilation of plant, reduce the efficiency of photosynthesis in flag leaves, and inhibit the plant growth. The study on the mechanism of nitrogen deficiency tolerance in the ScmiR393-overexpressed transgenic rice, and the exploration on the biological function of sugarcane ScmiR393 under the nitrogen deficiency stress, could provide theoretical basis and key gene elements for the breeding of sugarcane varieties with high nitrogen use efficiency.