The invention relates to a fully biologically degradable poly lactic acid / starch composite material, the composite material is composed of PLA (poly lactic acid) and the polymer thereof, starch, surfactant and coupling agent or compatibilizer and processing agent. The contents of the components are: 10-80 percent of PLA, 10-80 percent of starch, 0-3 percent of coupling agent, 2-20 percent of compatibilizer and 0.05-5 percent of processing agent. The surfactant, coupling agent and compatibilizer which have feature structures can change the dispersion of starch in the PLA, adjust and enhance the interphase compatibility of the PLA-starch blend system, strengthen the interaction among the composing substances, enhance the stability of the structure of PLA-starch interface blend, improve the mechanical performance of the composite material and the processing performance. The fully biologically degradable poly lactic acid / starch composite material can be used to produce panels, vessels, blank sheets, film, bands, wires and other products in particular shapes by injection moulding, extrusion moulding, press moulding, blow moulding, hot moulding, and the like, and the material is extensively applied to the fields of packaging, agricultural film, domestic and medical products, and the like.