The invention relates to good plasticity mold core molding sand, which is prepared from the following raw materials by weight: 20-30 parts of chromite sand, 10-14 parts of bauxite, 15-20 parts of brown corundum powder, 6-8 parts of alpha-Al2O3 micro-powder, 2-3 parts of sodium tripolyphosphate, 1-2 parts of dimethyl silicon oil, 4-5 parts of a furan resin, 14-18 parts of poly carbosilane powder, 220-240 parts of clay, 2-3 parts of fatty acid sodium, 4-5 parts of potassium methyl silicate, a proper amount of water, and 20-30 parts of an auxiliary agent. According to the good plasticity mold core molding sand, the clay is used, such that the matching cost is low, the chilling effect is good, and the gas permeability is good; the alpha-Al2O3 micro-powder is added, such that the plasticity is good, the thermal conductivity is good, the molding sand is suitable for mold core manufacturing, and the cast hole shrinkage and dispersed shrinkage solving effect can achieve more than 90, and the cast yield can be increased; the auxiliary agent of the present invention adopts alumina and other high temperature resistance materials, such that the auxiliary agent can not melt during casting, the adhesion of the clay particles can be prevented, and the recycling is easily performed; and the clay is wrapped on the surface, and the binding force with the clay particles is strong.