The invention discloses a mixed milk replacer and a preparation method thereof; the mixed milk replacer comprises the following raw materials in parts by weight: 16-20 parts of hulled corn, 15-20 parts of extruded corn, 6-10 parts of flour, 3-5 parts of white fish meal, 4-8 parts of debarked bean pulp, 2-5 parts of chyle fat powder, 2-3 parts of fermented bean pulp, 5-10 parts of whey powder, 3-6 parts of milk powder, 1-3 parts of white sugar, 2-3 parts of glucose, 0.4-0.5 part of monocalcium phosphate, 0.012-0.015 part of calcium formate, 0.01-0.03 part of high-temperature protease, 0.2-0.5 part of amino acid, 2-5 parts of thermostable amylase and culture thereof, 0.04-0.06 part of decavitamin and 0.2-0.6 part of compound microelements. The raw materials are mixed after being prepared to have the particle diameters of 2.0-3.0 mm and 10-15 mm; the mixed milk replacer pays attention to weak piglets and healthy piglets, reduces the feed waste, improves the food calling capacity and the food consumption, modifies the daily gain, and reduces the phenomena of negative gain and growth retardation caused by the weaning stress.