The invention discloses a reagent for causing a targeting effect of marrow mesenchymal stem cells on myocardial infarction focus, and its preparation method. The reagent is composed of a culture medium for causing a targeting effect of marrow mesenchymal stem cells on myocardial infarction focus, and marrow mesenchymal stem cells. The culture medium comprises solutes and a solvent. The solutes comprises the following seven components of 4.0 to 5.0 g/L of glucose, 0.11 to 0.19 g/L of sodium carbonate, 0.584 to 0.702 g/L of L-glutamine solution, 100 to 130 ml/L of dimethyl sulfoxide, 50 to 67 g/L of transferring, 5 to 6.6 g/L of insulin, and 0.01 to 0.05 g/L of basic fibroblast growth factor, wherein a concentration of each one of the components is a final concentration. The solvent is injection water. The reagent can cause a targeting effect of marrow mesenchymal stem cells on myocardial infarction focus and solves the problem that at present, through an intracoronary injection way, a small number of cells are leaved.