The invention relates to a method for amplifying mesenchymal stem cells on a large scale, and discloses an optimized method for amplifying mesenchymal stem cells in micro-carrier low serum manner by a bioreactor. The method can efficiently culture a lot of mesenchymal stem cells, and the mesenchymal stem cells obtained are good in activity. The method provided by the invention is suitable for large-scale fermentation production, and a lot of mesenchymal stem cells can be obtained within a short time, so that the method is used for experimental researches, tissue engineering and the like.