The invention relates to a rooting promoting liquid fertilizer, and a preparation method and application thereof. The rooting promoting liquid fertilizer comprises the following raw materials: a macroelement fertilizer, a microelement fertilizer, a compound amino acid, potassium dihydrogen phosphate, a plant growth regulator, chitosan and a water retaining agent, wherein the weight ratio of the plant growth regulator to the potassium dihydrogen phosphate is 1:(1000-2500). The invention also provides the preparation method and application of the rooting promoting liquid fertilizer. The liquid fertilizer disclosed by the invention is comprehensive in nutritional ingredients and is suitable for nutrition requirements of various crops in growth periods, the growth of root systems can be obviously promoted, soil can be improved, the disease resistance and the stress resistance of the crops are enhanced, and the target of reducing the fertilization amount is achieved.