The invention relates to a lithium battery electrolyte-resistant halogen-free flame-retardant polypropylene reinforced composite material which is characterized by containing the following components in parts by weight: 30-85 parts of polypropylene alloy, 5-20 parts of glass fiber, 10-40 parts of halogen-free flame retardant, 0.1-10 parts of oligomer, 0.1-10 parts of metal oxide and 0.1-10 parts of processing assistant. The preparation method comprises the following steps: (1) preparing the halogen-free flame retardant master batch: uniformly mixing components of the halogen-free flame retardant, adding into an internal mixer, adding the oligomer, uniformly mixing, performing devolatilization treatment, and granulating; (2) preparing the polypropylene alloy: uniformly mixing components of the polypropylene alloy, performing melt extrusion, and granulating; and (3) preparing the composite material: uniformly mixing the prepared polypropylene alloy, the prepared halogen-free flame retardant master batch, the metal oxide and the processing assistant, adding into a double screw extruder, performing melt blending and extrusion, drawing, and granulating.