In the study, effects of seed dressing with bio-fertilizer and decreasing nitrogen fertilizer input on the yield and quality of oat（Avena sativa L.） were studied in Baicheng City, Jilin Province. Five treatments were es-tablished using oat Baiyan 2 as experimental material, i.e., A1: with 90 kg N·hm^-2（CK）; A2: with 67.5 kg N·hm^-2;A3: with 45 kg N·hm^-2; A4: with 22.5 kg N·hm^-2; A5: without nitrogen fertilizer. Except of A1, others were seeddressed with bio-fertilizer. Results indicated that seed dressing with bio-fertilizer 30 kg·hm^-2could be the alterna-tive to 22.5 kg N·hm^-2. Treatment A2 showed the best comprehensive effect among five treatments, which had 5.7% larger spikelet number, 2.21% higher thousand seed weight, 3.98% higher the relative feed value, 1.99% lower neu-tral detergent fiber（NDF） content and 2.17% lower acid detergent fiber content than treatment A1. Also, no obvious difference（p＞0.05） in grain yield was observed among five treatments. Moreover, compared with treatment A1, treat-ment A2 increased grain crude protein content and fat content by 4.58%（p＞0.05） and 0.22%（p＞0.05）, respectively.Furthermore, there was no significant difference（p＞0.05） in grain and straw nitrogen, phosphorus and potassium contents among five treatments.