The invention discloses an improved soil overturning and ploughing machine for improving farmland soil. The soil overturning and ploughing machine comprises a traction frame, a rack fixedly connectedto the rear part of the traction frame, a deep-layer stirrer, a shallow-layer stirrer, a speed change mechanism fixed to the middle of the rack, a first transmission mechanism connected between the speed change mechanism and the deep-layer stirrer, and a second transmission mechanism connected between the speed change mechanism and the shallow-layer stirrer, wherein the deep-layer stirrer and theshallow-layer stirrer are arranged at the lower part of the rack. The improved soil overturning and ploughing machine has the advantages of being convenient and reliable to operate and can achieve uniform mixing of soil on the upper and lower layers and concentration dilution of heavy metal. The improved soil overturning and ploughing machine has great popularization performance, can be used for conducting deep overturning and applying fertilizer at the same time, realizes soil environment improvement, guarantees the quality of agricultural products, and is more applicable to soil restorationengineering. Deep-tillage cutters are munted on the deep-layer stirrer at the front part of the machine in a staggered mode, the soil depth of deep tillage can reach 50 cm when the machine moves forwards, and after the soil is loosened, the shallow-layer stirrer carries out secondary stirring on the soil in the depth of 20 cm, so that shallow-layer soil and deep-layer soil are fully mixed, and concentration dilution of the heavy metal is achieved.