The invention relates to a preparation method of potassium humate containing an algae active component. The method includes the following steps: grinding dried algae into powder, and placing the algae powder in a fermentation tank and performing sterilization; preparing seed liquids of two bacterial strains, and inoculating the seed liquids onto the algae base material in several times to achieve stepwise fermentation; after fermentation, press-filtering the product to obtain an algae liquid, adding a humic acid raw material and potassium sulfate, regulating pH value by KOH, and performing a stirring reaction under 1.5-2.0 normal atmospheric pressures at a constant temperature of 60 DEG C for 2-3 h; and filtering a reaction product, and concentrating, drying and crushing the product to prepare the product. The composite stepwise fermentation technology is better than single bacterial strain fermentation and common multi-bacterial strain mixed fermentation in technical effects. The method is high in fermentation efficiency, is short in time and has strong controllability in the whole process. The product contains an algae active component brown algae oligosaccharide, a plant growth regulator and a large amount of microelements, which are combined with the potassium humate as an active component, so that the product has significant effects on improvement of stress resistance and disease resistance of crops, thereby satisfying demands in modern agriculture.