Based on long-term (2017—2022) positioning experiments, five experimental treatments were set up which included nitrogen phosphorus potassium balanced application as control (CK), straw direct return under nitrogen phosphorus potassium balanced application (SR), wheat straw + corn straw biochar returning to field (WM_BC), corn straw + wheat straw biochar returning to field (W_BCM), and wheat and corn straw biochar returning to field (S_BC), and the effects of long-term different straw return forms were explored on physicochemical properties and shrinkage characteristics of typical lime concretion black soil. The results showed that SR was beneficial for increasing the contents of soil alkali hydrolyzed nitrogen and available phosphorus, while straw and biochar application were more beneficial for increasing soil available potassium and total nutrients, and W_BCM had a more significant effect; Returning straw to the field promoted the fragmentation of large aggregates with a diameter of >5 mm (excluding S_BC), and the fragmentation of WM_BC large aggregates formed a more evenly distributed soil structure; Long term straw and biochar returning to the field significantly reduced soil bulk density and increased soil porosity, with W_BCM being superior to WM_BC; The field water capacity of SR was the highest, followed by W_BCM. In conclusion, returning straw and biochar to the field is not only beneficial for improving the nutrients of lime concretion black soil, but also significantly reducing its bulk density and increasing its porosity. And long term straw returning can alleviate soil shrinkage, with WM_BC having the best effect, followed by W_BCM.