This study aimed to provide foundational data for breeding new high-yielding and early-maturing oat varieties suitable for domestic environments by evaluating the quantitative and qualitative traits of 481 oat accessions and selecting elite lines. Descriptive statistics and diversity index analyses revealed a wide range of genetic variation in traits related to heading date, flag leaves, and panicles. Correlation analysis of the major agronomic traits revealed distinct positive correlations among yield-related traits, including plant height, leaf size, and panicle length. Based on key agronomic traits, principal component analysis (PCA) demonstrated that the first and second principal components accounted for 78.4% of the total phenotypic variation. Finally, 36 elite accessions were selected based on three combined traits: biomass, yield potential, and early development. Among them, seven double elite lines (OG318, OG317, OG113, OG523, OG289, OG320, and OG117) exhibited significantly taller plant heights, longer panicle lengths, and higher biomass, making them highly suitable for breeding high-yielding varieties. Notably, the single elite lines, ‘OG391’ and ‘OG204’, demonstrated early-maturing characteristics while maintaining yield potential comparable to that of the standard variety, making them highly valuable resources for the domestic double-cropping system. Overall, the selected elite lines will serve as valuable crossing parents for future oat breeding programs.