Abstract: Soil conditioners have been applied in agriculture due to advantages, such as coordinating soil water and fertilizer, improving soil water-retaining and fertility-reserving capacity. A new type of liquid conditioner was introduced in oat cultivation in this study, its’ effects on soil physical properties, and characteristics of soil organic carbon and nitrogen, and oat yield under nitrogen fertilizer reduction were investigated to explore the driving mechanism of N reduction by conditioners on crop yield and soil nutrients. Five treatments were set: no fertilizer (CK), 80% N fertilizer (N₈₀), regular N application (N₁₀₀), conditioner + 80% N fertilizer (PN₈₀), and conditioner + regular N application (PN₁₀₀). The results showed that the fertilizer + conditioner treatments differed from the single fertilizer treatments in terms of physical properties, carbon and nitrogen contents, and oat yield. The treatments with conditioner (PN₈₀ and PN₁₀₀) significantly increased soil water content, field capacity, porosity, and reduced soil bulk density compared with the treatments with only fertilizer. Furthermore, the nitrogen reduction of 20% (N₈₀) significantly increased soil porosity and reduced soil bulk density compared with conventional nitrogen application (N₁₀₀). The study showed that 20% N reduction had varying degrees of inhibition on organic carbon, total nitrogen, and its components in different soil layers. Furthermore, the addition of the conditioner significantly increased organic carbon, total nitrogen, nitrate nitrogen, active organic carbon, and microbial carbon in the 0–60 cm soil layer and 20−60 cm soil layer compared with the treatments with N fertilizer alone. The effect of the PN₁₀₀ treatment was the most significant. The effects of different treatments on the nutrients and yield of oats varied greatly, with that of the PN₈₀ treatment being the most significant. Compared with N₁₀₀, the total N, P, and K contents and crop yield of oats in PN₈₀ significantly increased by 12.93%, 15.16%, 3.69%, and 18.73%, respectively (P<0.05). Compared with N₁₀₀, N₈₀ significantly reduced N, P, and K uptake in oats at 20% N reduction, but did not cause yield reduction in oats. In conclusion, compared with conventional fertilization, N₈₀ with a soil conditioner improved soil properties, increased soil carbon content, reduced the risk of nitrate N leaching, and significantly increased the nutrient uptake and yield of oat. The effect of 80% N fertilizer + soil conditioner on the nutrient content and yield of oats was the most significant, while the treatment with 100% N fertilizer + soil conditioner was the most effective in improving soil nutrient content. This is essential to realize the green development of agriculture, reduce the environmental impact of fertilizer input, and improve the utilization rate of nitrogen fertilizers.