Poor interfacial properties and uncontrollable phase morphology encountered during the fabrication of poly(butylene adipate-co-terephthalate) (PBAT)/thermal plastic starch (TPS) biocomposites, result unfortunately in low mechanical performances and thus limit its applications. Here an approach in terms of phase morphology controlling, i.e., extrusion compounding followed by oscillation shear injection molding (OSIM), is proposed to construct in-situ TPS fiber and skin-core structure consisting of TPS fiber and droplet in skin layer, and spherical TPS in core layer, which tremendously benefits the mechanical properties. Specifically, the tensile strength, modulus and ductility for the biocomposites with various loadings of TPS, even when TPS loading as high as 55 wt %, outperform pure PBAT sample fabricated by conventional injection molding (CIM) with the increment of 51%, 308% in strength and modulus, respectively. Meanwhile, the elongation at breakage can maintain at 196%. The unprecedented establishment of high-performance PBAT/TPS biocomposites is in great need for potential applications, such as green packaging.