The invention relates to a method based on 25 current space vectors for modulating a DC source, thus simplifying the modulating control mode of a current mode multilevel inverter and reducing the technical problem of complexity processing. The technical scheme adopted by the invention is that the method is realized by means of a CPU and supporting management software procedures, wherein the CPU uses a first memory cell with reference vector and a second memory cell with the corresponding sampling period to calculate and control the modulation time; and the method is to code and rank the 25 space vectors and form a special database. The method comprises the following steps: forming basic space vectors, selecting space vectors, determining the output sequence of the vectors, calculating thetime of each vector, performing switch output for each vector, uniformly coding the selecting principle of the space vectors and the output sequence of the vectors, storing the coding result in a memory, and, calling the corresponding space vectors from the memory in run-time according to the judgment result of sectors and areas. The method is fast, convenient and simple.