In this paper, LiMn2O4 was synthesized by the microwave-template method, and the synthesis mechanism was studied by the in-situ FTIR. It was confirmed by the FTIR that polyacrylamide was decomposed gradually during the spinel LiMn2O4 preparation, and there was some chemical bond between the reactants and polyacrylamide in the precursors. Polyacrylamide acted as template in the course of the preparation of precursors and forming of spinel lithium manganese oxide compound. As a result of the certain chemical bond, the controlling and adjusting of the LiMn2O4 crystalline were realized, so that agglomeration and lacunae framework of the spinel was adjusted.