The invention discloses a double-chelate liquid fertilizer. The double-chelate liquid fertilizer comprises a sugar alcohol chelating agent, an organic polymer chelating agent, medium trace element salt, medium trace element oxide, KOH and water. The preparation method comprises the following steps of: weighing the sugar alcohol chelating agent, and the organic polymer chelating agent according to a proportion, and dissolving into water; adding KOH to prompt the dissolving of the chelating agents, and dissolving for 5-10min; weighing the medium trace element salt and the medium trace element oxide according to the proportion, dissolving into the solution, and stirring; reacting at a constant temperature until the solution is clear, so as to obtain the double-chelate liquid fertilizer. With the sugar alcohol and organic polymer as the chelating agents, compared with double chelating employing single sugar alcohols or amino acids, the direct absorbing and using of crops are guaranteed, the organic polymer chelate is stable, the sugar alcohol chelate is absorbed fast, the organic polymer chelate can be released slowly, and by the cooperation of both, the purpose of synergistic interaction of rapid and medium effect release of medium trace elements can be achieved.