The invention discloses a full-water-soluble organic-inorganic compound fertilizer, which comprises potassium fulvate, ammonium sulfate, monopotassium phosphate, anhydrous magnesium sulfate, metalloproteinase and Jikang enzyme. The Jikang enzyme is prepared by the following steps: uniformly stirring and mixing 100 parts of plant acid, 600 parts of amino acid and 5 parts of an amino acid surfactant; adding 100 parts of mineral source fulvic acid and 150 parts of humic acid, fully stirring and uniformly mixing all the components, adding the mixture into a fermentation tank, inoculating a microbial agent for cultivation for 18 hours, and finally adding 15 parts of chitosan and 10 parts of subtilisin, and uniformly mixing all the components for obtaining the Jikang enzyme. The invention also discloses a preparation method of the fertilizer, which comprises the following steps: preparing metalloproteinase, and mixing the raw materials. The compound fertilizer is a biological, organic and inorganic combined fertilizer, organic components (fulvic acid) in the fertilizer form colloidal substances in soil, the formation of a soil aggregate structure can be effectively promoted, and the water, fertilizer, gas and heat conditions of the soil are coordinated.