The invention provides a preparation method of full-alkaline synthetic melamine urea-formaldehyde resin and a wood impregnation method thereof. The preparation method comprises the following steps: adding 900-1200 parts by weight of a formaldehyde solution, 4-8 parts by weight of a sodium hydroxide solution, 20-120 parts by weight of melamine and 225-500 parts by weight of urea, then adjusting thetemperature to 60-90 DEG C, carrying out a constant-temperature reaction for 0.5-5 hours, and keeping the pH value to be 7-10; keeping the temperature of the constant-temperature reaction to be 60-90DEG C, then adding 150-475 parts by weight of urea and 90-300 parts by weight of maltodextrin or polyvinyl alcohol or starch, and carrying out a reaction for 0.5-5 hours; and adding 10-300 parts by weight of ammonia water and 2-30 parts by weight of triethylene tetramine, carrying out stirring for 5-20 minutes, and carrying out cooling to room temperature for discharging. During use, wood blocksobtained after log sawing are put into a kiln for drying, sodium borate, ammonium borate and quaternary ammonium copper are added into the melamine formaldehyde resin impregnation liquid obtained by the method, adding the dried wood blocks into the mixed solution obtained by the method for impregnation; and drying the impregnated wood block samples to finally obtain a finished product.