The present invention provides a mesenchymal stem cell injection, a preparation method thereof, and application thereof in preparing diabetes mellitus drug. Mesenchymal stem cells used by the present invention come from the human umbilical cord and the human placenta. The ingredients of the mesenchymal stem cell injection are: mesenchymal stem cells, human albumin, low molecular weight heparin, a compound amino acid, vitamin C, and a solution medium. The solution medium is a compound electrolyte solution, glucose water, or a normal saline solution.
