The study of genetic diversity in oat germplasm resources not only contributes to the collection and evaluation of germplasm resources, but also has important guiding significance for the production and breeding of oats. This study analyzed the diversity, variation, and clustering of 20 morphological traits in 260 oat germplasm resources, evaluated the genetic variation level of their morphological traits, and clarified the characteristics and genetic diversity of oat germplasm resources, aiming to provide a basis for oat germplasm innovation and variety improvement. The results showed that there was a significant genetic diversity of morphological traits in the 260 oat germplasm resources. The genetic diversity index of quality traits was the highest in grain color (1.53) and the lowest in awn color (0.76). The genetic diversity index of the 12 quantitative traits was normally distributed, and the genetic diversity index of quantitative traits was the largest in thousand grain weight (2.03) and the smallest in effective tillers (1.22). The highest coefficient of variation was the effective tillering number (89.02%), and the lowest was the plant height (11.19%). According to genetic difference of each characteristic varieties, the 260 accessions should be classified into 6 categories by cluster analysis. Germplasm group I includes 42 materials which can be used as parent materials for seed type selection purposes. Germplasm group II has 31 materials that can be used as parent materials for breeding high-yield forage varieties. Germplasm group IV includes 41 materials that can be used as breeding materials for breeding large grain specific varieties. Germplasm group V includes 46 materials that can be used as parents for oat dwarfing. Germplasm Group III includes 46 materials, while Germplasm Group VI includes 54 materials, and the comprehensive properties of these two germplasm groups were not outstanding. This study can provide theoretical basis for the protection, development and utilization of oat germplasm resources in eastern Inner Mongolia.