The invention relates to a rare earth humic acid complete compound fertilizer and a preparation method thereof. The complete compound fertilizer comprises the following components: rare earths, urea, diammonium phosphate and/or monoammonium phosphate, potassium nitrate and/or potassium chloride and/or potassium sulfate, silica, calcium dioxide, magnesium oxide, zinc sulfate, manganese sulfate, ferrous sulfate, copper sulfate, borax, ammonium molybdate, and humic acid. The preparation method consists of: mixing the nitrogen fertilizer, phosphate fertilizers and potassium fertilizers, spraying 1-5 parts of water to prepare a slurry, adding rare earth and the remaining materials, stirring the materials evenly, and carrying out granulation and drying, thus obtaining the rare earth humic acid complete compound fertilizer. The invention also provides application of the compound fertilizer in plant cultivation. The compound fertilizer provided by the invention has the existing fertilizers lacked advantage of supply of comprehensive nutrient elements to plants.