The present invention provides a method for rebuilding a marrow microenvironment in a testee whose marrow microenvironment is damaged. The method comprises : implanting a composition containing separated mesenchymal stromal cells (MSC) into a marrow cavity of a testee. By means of the method in the present invention, the marrow microenvironment is rebuilt, the normal marrow hematopoiesis function is recovered, the leukemia pathology progress is inhibited/delayed, and the survival period is obviously prolonged. In addition, the method in the present invention can be used for treating blood tumors such as leukemia and Aplastic anemia (AA) and has the advantages of being safe, effective and free of side effects.