The invention relates to the field of polymer materials, in particular to a flame-retardant and antibacterial PLA (polylactic acid) biodegradable composite for 3D (three dimensional) printing. The composite is prepared from the following raw materials in parts by weight: 100 parts of PLA, 2-10 parts of a nucleating agent, 5-10 parts of a natural macromolecule antibacterial agent, 1-5 parts of a toughening agent, 0.3-0.8 part of an antioxidant, 0.5-1 part of a compatibilizer, 0.5-1.5 parts of a lubricant and 5-10 parts of a DOPO (9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide) derivative flame retardant. According to the flame-retardant and antibacterial PLA biodegradable composite for 3D printing, the DOPO derivative flame retardant and the natural macromolecule antibacterial agent are added to a PLA composite system, so that on the one hand, the PLA composite is endowed with a lasting and broad antibacterial property by the natural macromolecule antibacterial agent, bactericidal power is high, performance is stable, biodegradation is facilitated, and secondary pollution can be prevented; on the other hand, when content of the flame retardant reaches 5%-10%, a cured product can reach the level of UL94, V-0.