[Objective] This paper studied the effects of straw returning on soil nitrogen and microbial biomass carbon and nitrogen contents in different soil depths to provide scientific basis for improving the efficiency of returning straw.[Methods] Five different treatments were labeled as control CK(no straw), T₀(surface coverage), T₁₀(10 cm returning field), T₂₀(20 cm returning field), T₃₀(30 cm returning to the field).[Results] ① Compared with the control, the contents of soil organic matter, total nitrogen and nitrate nitrogen in straw returning treatments increased 3.98%~29.36%, 2.72%~45.52%, 10.48%~56.64%, respectively. The contents of ammonium nitrogen decreased about 7.75%~39.20%. ② The straw returning treatment had a significant effect on soil microbial biomass. Compared with the control, the soil microbial biomass carbon and nitrogen increased 5.01%~35.78%, 9.69%~52.56%, respectively. ③ Principal component analysis method was used to evaluate the soil quality with different straw returning treatments. The comprehensive score order was CK < T₃₀ < T₀ < T₂₀ < T₁₀. When the straw returned to the field at 10 cm and 20 cm depth, labeled T₁₀ and T₂₀ treatments, had more significant effects on soil nitrogen levels and microbial biomass carbon and nitrogen contents than other treatments had, and the treatment effect of 10 cm straw returning was most obvious.[Conclusion] Straw returning could increase soil nitrogen and microbial biomass carbon and nitrogen content, improve soil traits. Better effects for 10 cm and 20 cm depths of straw returning were found, especially for 10 cm depth straw returning, and its effect were the most significant in soil nitrogen and microbial biomass carbon and nitrogen.