The invention belongs to the technical field of a hydroponic lettuce nutrient solution, in particular to a lettuce nutrient solution formula and a preparation method thereof. The lettuce nutrient solution formula comprises the following components: fertilizer A: 286g/T of calcium nitrate; fertilizer B: 454g/T of potassium nitrate, 163g/T of magnesium sulfate and 87g/T of ammonium dihydrogen phosphate; fertilizer: 22g/T of EDTA iron, 3.1g/T of boric acid, 2.2g/T of manganese sulfate, 0.55g/T of zinc sulfate, 0.09g/T of copper sulfate and 0.1g/T of ammonium molybdate; and organic acid: 410-460g/T of citric acid or 280-320g/T of malic acid or 280-320g/T of tartaric acid. According to the nutritional needs of lettuce hydroponics, a large number of elements and trace elements are used in balance; miscellaneous preparation processes are simplified according to the actual operation needs; and nutrient solution raw materials are all in solid package, and the nutrient solution is prepared on the spot and is more appropriate for the requirements of family culture.