The invention discloses a fulvic acid water retention plant seed growth additive and a preparation method thereof. The fulvic acid water retention plant seed growth additive comprises the following raw material components by weight: 10-20 parts of compound sodium nitrophenolate, 5-20 parts of an active organic mixture, 5-15 parts of biomass particles, 1-15 parts of fulvic acid, 3-9 parts of an amino acid mixture, 1-6 parts of brassinolide and 80-100 parts of water. The additive provided by the invention can accelerate the growth speed of plants, break dormancy, promote growth and development,prevent flower and fruit dropping, fruit cracking and fruit shrinking, improve the product quality, increase the yield, and improve the disease resistance, insect resistance, drought resistance, waterlogging resistance, cold resistance, salt and alkali resistance, lodging resistance and other stress resistant capabilities of crops.