The invention relates to a manufacturing method of a high density fiberboard for a whitened type E1 grade floor substrate, which comprises the steps of wood chipping and screening, pre-stewing and stewing, defibrator process for causing fiber separation, concoction of E1 grade urea formaldehyde resin glue, curing agent preparation, the application of urea-formaldehyde glue, curing agents and paraffins, drying, paving, hot pressing, cooling and tempering, and sanding and saw cutting, and is characterized in that woods are selected from major diameter cottonwoods with diameters larger than 8cm, are evenly chipped and are then placed in an outdoor storage yard to be fermented for 5 to 15 days; in the concoction process of the E1 grade urea formaldehyde resin glue, urea is added at 5 times; and the curing agents are formed by preparing phosphoric acid accounting for 3 to 5 percent of the total content, urotropin accounting for 1 to 3 percent of the total content, triethanolamine accounting for 1 to 3 percent of the total content, and ammonium sulfate accounting for 19 to 21 percent of the total content. The obtained whitened type E1 grade floor substrate has the advantages of little surface impurity, fine and smooth fiber, white color, good visual effect, reasonable density distribution and moderate intensity, and is frequently used for producing top grade indoor laminate flooring and composite floors.