When the modulation algorithm of the space vector in a multilevel inverter was rotated by 45°, the concepts of characteristic network using basic vectors to track the reference vectors, characteristic quadrangle and vectors basic switching were obtained. On the basis of the switching relation between the "closed routes" of characteristic quadrangles, we chose the pervertex of each sector in the basic switching traversal characteristic network. Then, we got the least switching times in the modulation algorithm of space vectors in multilevel inverters. Based on a 2cell 5level inverter, according to the reference voltage variation, we have found that the characteristic network can be divided into two types and have given the corresponding algorithms of switching times. Compared with the simulation result, it has been shown that this algorithm is correct. And compared with the phase disposition sinusoidal modulation (PD SPWM) method, the total switching times in one reference voltage period of the proposed modulation algorithm is only 38% of PD SPWM. The simulation output voltage waveform is quite close to the reference voltage.