Mutual-cell voltage imbalance is an inherent and critical problem for the cascaded converter, which has been found the vital industrial application. A novel space vector pulse width modulation(SVPWM) algorithm is presented to address the mutual-cell voltage imbalance issue on the premise of internal-cell voltage balancing for the cascaded three-level converter in this paper. It introduces the specific implementation process of the proposed algorithm in detail including the way to choose the effective space vectors distributed in 3-D space and the equalizing principle. Compared with previously generalized solutions, it has the great capacity to balance the mutual-cell voltage imbalance without any jumping phenomenon of input voltage of each module under the condition of loads mutating. It is so simple, flexible and finally verified by the simulation and experiment.