Abstract: Straw returning has widely been used in circular agriculture and soil conservation tillage in recent years. This study aims to explore the decomposition impacts of the wheat stalk under three tillage modes on the paddy filed in the summer rice and winter wheat system. A field experiment was conducted at the Shajiang black soil zone in the middle-lower reaches of Huaihe River. Three tillage treatments were set in the paddy filed, including "ploughing+rotary+puddling (PRP)", "rotary+puddling (RP)", and "puddling+rotary (PR)". The decomposing parameters were then measured, such as the decomposing rates, the residual contents of the wheat stalk nutrients and components from 0 to 90 days (45 days as step length). A laser confocal scanning microscopy (OLS-4100, Olympus) was selected to characterize the microstructure of wheat stalk. The results showed that: 1) The decomposition rate varied fast in the early stage, but slowly in the late stage. Specifically, the decomposition rate rapidly reached 45%-55% during 0-45 days, while the maximum value of the decomposition rate was less than 58.27% under different tillage and straw returning modes at 90 days. 2) There were significant effects of returning time on the parameters, such as wheat stalk nutrients (including carbon (C), nitrogen (N), phosphorus (P), and potassium (K)), micro structures (including radial or X-direction length (Lx), axial or Y-direction length (Ly)), and mechanical properties (including shearing strength (SS), bending strength (BS), compressive strength (CS)) (P<0.05). The influence of returning time was found on the wheat stalk components (including Lignin (L), cellulose (Ce), Hemicellulose (He)). The residual contents of the wheat stalk components and nutrients such as C, N, P, L, and He increased to 1.01-1.33, 1.81-3.45, 1.15-1.82, 1.15-1.39, 1.45-2.77 times than those of the indexes at 0 day. Meanwhile the residual contents of the wheat stalk K and Ce decreased to 0.04-0.11, 0.77-0.95 times than those of the indexes at 0 day. The Lx and Ly of micro-structure parameters were 5.65-13.60, 2.48-9.18 times than those of the indexes at 0 day. The wheat stalk SS, BS, and CS at 45 and 90 days would decreased to 0.07-0.34, 0.26-0.58 and 0.43-0.76 times than those of the initial parameters at 0 day. 3) There were significant effects of tillage on the residual contents of the wheat stalk N, P and K (P<0.05), while impacts on the residual contents of the wheat stalk L, Ce and He. Comparing with the treatment of RP and PR, the treatment of PRP rapidly reduced the residual contents of the wheat stalk N, P, K, and Ce, but quickly increased residual contents of the wheat stalk L, while there was no reasonable order of residual He. Consequently, the PRP treatment presented a better performance for straw degradation in this case. This finding can greatly contribute to reduce the mechanical strength of wheat stalk and release nutrients when returning wheat straw to the field in sustainable agriculture.