The invention provides a manufacturing method of a non-formaldehyde solid wood composite floor using low-density cottonwood veneers as base materials. The non-formaldehyde solid wood composite floor is at least a cottonwood base plate assembly manufactured by combining following two raw materials: first, cottonwood veneers formed by stewing cottonwood logs at a low temperature of 10 to 50 DEC C, then rotary-cutting or slicing the cottonwood logs and afterwards drying the cottonwood logs, and second, plastic adhesive films manufactured by adopting thermoplastic resin; the treated cottonwood veneers are coated with coupling agents and are then assembled with the plastic adhesive films, and after hot-pressing and setting treatment, a cottonwood base plate is manufactured; afterwards, decorative thin wood is adopted as a surface layer and is combined with the cottonwood base plate assembly, and after cold-pressing, a floor blank is manufactured; and finally, the floor blank is milled, tenoned, slotted, and subjected to paint curing, and then a product is manufactured. Through using high polymer materials, from which no harmful substance escapes, in both the machining process and the use process, the environmentally friendly solid wood composite floor is produced.