Abstract: Oat is an important crop for food and feed in China. The construction of oat mutant library will be important for the study of functional genomics and genetic improvement of oat. In this study, seeds of oat Huazao 2 was treated by chemical mutagen Ethyl methane sulfonate(EMS). A total of 4083 individual plants were obtained in M1. Biological characters and agronomic traits were investigated and phenotypic mutants were identified in M2 , which selected 2000 individuals among 4083.Two etiolated seedling mutants identified from M2 were validated through M3. The results showed that great phenotypic variation appeared after EMS treatment. A total of 196 mutant plants were screened out in M2 with 9.8% of mutation rate of phenotypes including seedling habits, leaf appearance, plant height, spike and maturity. It was proved that the etiolated seedling mutation was steadily inherited in M3. This study has established the EMS mutagenesis system and identified various mutant types, which will provide a basic material for the study of functional genomics and genetic improvement of oat.