The invention discloses a fully-water-soluble medium-trace element fertilizer containing biostimulant and a preparation method thereof, belonging to the technical field of fertilizers. The fertilizerand the preparation method thereof in the invention solve the technical problems that medium-trace elements are easy to fix and lose in soil and the absorption and utilization rate of medium-trace elements by crops is relatively low in the prior art. The fully-water-soluble medium-trace element fertilizer containing the biostimulant is prepared by mixing medium-trace element raw materials, biostimulant raw materials and an auxiliary agent. The fertilizer comprises the following raw materials in parts by weight: the medium trace element raw materials consisting of 5-10 parts of chelated calcium, 4-8 parts of magnesium sulfate heptahydrate, 3-9 parts of ferric sulfate, 2-8 parts of zinc sulfate, 2-5 parts of manganese sulfate, 0.5-1 part of copper sulfate, 0.05-0.1 part of ammonium molybdateand 1-3 parts of sodium borate decahydrate, the biostimulant raw materials consisting of 15-30 parts of potassium fulvate, 10-20 parts of sodium alginate, 15-20 parts of amino acid and 10-15 parts ofpotassium silicate, and 0.1-0.5 part of the auxiliary agent. The fully-water-soluble fertilizer has an improvement effect on crops and soil, can improve the absorption and utilization rate of medium-trace elements, and enables the overall quality of crops to be improved.