The invention discloses a method for preparing an active algae extract foliar fertilizer. The method comprises the following steps: using natural algae as a raw material, grinding in a dilute acid solution with PH2-4 and homogenating; then, adding cellulase and pectinase to carry out enzymolysis, centrifuging collected filtrate to remove non-soluble impurities, carrying ultrasonic degrading to obtain small-molecular substances , subsequently concentrating, regulating the PH value to 5.0-7.0, inoculating pre-cultured probiotic bacteria, conventionally fermenting, and using fermented pulp as the active algae extract foliar fertilizer. The foliar fertilizer has endogenous plant growth substances, such as plant auxin, cytokinin and gibberellin, has protein amino acids capable of being directly absorbed and used by plants as nutrients, other certain free amino acids, peptides, nucleotides and the like, and has algae polyphenols, flavonoid compounds, terpenoid compounds and the like. The plant resilience, such as drought resistance, cold resistance and disease and insect resistance can be enhanced under the condition of improving the yield.