The invention discloses a polypeptide-ammonium polyphosphate trace element liquid chelated fertilizer and a preparation method of the liquid chelated fertilizer. The polypeptide-ammonium polyphosphate trace element liquid chelated fertilizer comprises the components by weight percent: 5-25% of urea, 5-15% of ammonium polyphosphate, 5-25% of potassium nitrate, 0.2-3% of potassium silicate, 0.8-5% of potassium chloride, 0.008-0.1% of polyaspartic acid, 0.8-5% of ammonium sulfate, 0.8-5% of ethylene diamine tetraacetic acid (EDTA) calcium, 0.2-3% of EDTA magnesium, 0.02-1.5% of EDTA boron, 0.005-0.1% of EDTA zinc, 0.005-0.1% of EDTA iron, 0.005-0.05% of EDTA copper, 0.005-0.05% of EDTA manganese, 0.001-0.01% of nickel sulfate, 0.001-0.01% of ammonium molybdate, 0.0008-0.01% of cobaltous sulfate, 0.008-0.1% of polyacrylamide and the balance of water. The polypeptide-ammonium polyphosphate trace element liquid chelated fertilizer disclosed by the invention is simple in technology, scientific in proportion, balanced in fertilization, low in cost and good in effect.