The invention discloses a modified starch/lactic acid oligomer reactive blending total biolysis plastic. The modified starch/lactic acid oligomer reactive blending total biolysis plastic comprises plastic master batch that is used as raw material and an accessory ingredient. Mass composition of the plastic master batch: 2-50 portions of modified starch and 2-70 portions of lactic acid oligomer. The lactic acid oligomer that is synthesized by a one-step method is selected to go through continuous coextrusion together with the modified starch that has low cost by a solid phase condensation method, then auxiliary homotaxial or double-axis is provided for strengthening thermal stretch, thus obtaining the total biolysis plastic that has performance characteristics of being hard and tenacious and low price. The production cost, tensile strength, elongation at break and Young modulus of the total biolysis plastic are better than the existing relevant total biolysis plastic. The total biolysis plastic prepared by the invention can be applied in developing green consumables of high-tech electronic products, disposable packing materials, hotel articles, agricultural mulching film and so on, thus realizing greening of high-tech industries, releasing white pollution and saving deficient petroleum resource.