Abstract: In order to study the effects of different moisture contents and additives on the quality of baling oat silage, a 2×5 experiment was designed. Baling oat harvested at grain filling stage was wilted to target moisture contents (45%-50% and 65%-70%) and treated with corn flour (4%), urea (0.4%), Synlac Dry (0.002 g/kg), Sila-Max 200 (0.0025 g/kg), or directly baled without additives (CK). After 40 d ensiling, nutrition and fermentation were measured, and microbial counts and community analysis were undertaken by plate-culture. Moisture contents and additives had significant effects on silage quality. Compared with those at 45%-50% moisture content, treatments at 65%-70% moisture content had more stable CP, main organic acids and lactic acid bacteria (LAB), lower acid detergent fiber (ADF), neutral detergent fiber (NDF), water soluble carbohydrate (WSC) and mould and yeast (M&Y) counts, showing a better ensiling effectiveness. In contrast with CK, flour and urea treatments at 65%-70% moisture content had higher NDF, ADF and NH₃-N contents, but lower WSC. Sila-Max 200 led to the lowest NDF and ADF contents (52.12% and 32.14%, respectively), the highest lactic acid and significantly increased LAB, thus inhibiting aerobic microorganisms and achieving the best silage performance. In conclusion, adding suitable additives to oat with 65%-70% moisture content could signficantly improve the oat silage quality.