The invention discloses a manufacturing method of flame retardant solid composite floors. The method comprises steps of: performing flame retardant treatment on a natural rare tree veneer with the thickness of 0.5mm to 5mm by a vacuum pressure impregnation method, adhering the dried veneer to a glued floor substrate, and performing the processes of assembling, cold pressing, thermal pressing, health preserving, edge cutting, sanding, mortising and the like to obtain the solid composite floor blank; and then performing painting treatment on the surface of the solid composite plate blank, wherein the painting treatment adopts a process of twelve bottoms and two surfaces and the painting is performed according to the order: water primer, putty, elastic primer, wear resistant primer, transparent primer, sander, wear resistant primer, hardening primer, transparent primer, wear resistant primer, hardening primer, transparent primer, sander, finishing paint and finishing paint, and the wear resistant primer, the hardening primer and the sander are added with flame retardant agent. The flame retardant solid composite floor manufactured by the method has excellent flame retardant and fireproof performance and eco-friendly performance, and has excellent physics mechanical properties.