Abstract: In order to understand the effects of selenium（Se） and copper（Cu） trace fertilizers on the growth index, yield and nutrient composition of oat fresh grass and explore the appropriate base application amount of Se and Cu fertilizer, this experiment were divided into 5 treatments as the following: no fertilizer, Se fertilizer（57 mg/m~2）, Se + low Cu fertilizer（57 mg/m~2+78 mg/m~2）, Se + medium Cu fertilizer（57 mg/m~2+117 mg/m~2） and Se + high Cu fertilizer（57 mg/m~2+156 mg/m~2）. The sowing date of oat was October 1, 2018 and all fertilizers should be applied as base fertilizer before sowing. Plant height, single plant tillerings, stem to leaf ratio（S/L ratio）, fresh to dry ratio（F/D ratio）, forage yield and nutrients composition were measured in flowering period in next year of sowing. The results showed that compared with no fertilizer, the plant height and single plant tillerings of oat grass in base Se + low Cu fertilizer groups were increased by 6.77%（P＜0.05） and 19.10%（P＜0.05）, respectively, and the F/D ratio and S/L ratio of oat grass were decreased by 5.83%（P＜0.05） and 10.67%（P＜0.05）, respectively. In addition, the plant height and single plant tillerings in base Se fertilizer and Se + medium Cu fertilizer group were significantly increased（P＜0.05）, and the F/D ratio of oat grass in base Se + high Cu fertilizer group was significantly reduced（P＜0.05）. The yield of oat at flowering stage was increased by 11.57%（P＜0.05） and 6.02%（P＞0.05） by base application of Se fertilizer and Se + low Cu fertilizer at flowering stage, respectively. Basal application of Se + medium Cu fertilizer and Se + high Cu fertilizer could significantly increase CP and ADF contents（P＜0.05） and decrease Ca content of oat grass, respectively（P＜0.05）. The results indicated that basal application of Se and Cu trace fertilizer could affect growth index, forage yield and forage quality of oat. Basal application of Se + low Cu fertilizer was beneficial to yield increase, and basal application of Se + medium Cu fertilizer and Se + high Cu fertilizer was beneficial to improve nutrient quality.