In this paper, a novel spatial modulation (SM) scheme is proposed based on the constellation's set-partitioning. Specifically, the original digital constellation is divided into two sub-sets with each one having enlarged Euclidean distance between pair of constellation points. And the new SM transmission will activate two transmit antennas at the same time, and the digital modulation symbols from two activated antennas should be selected from two different partitioned sub-constellations, respectively. Analysis and simulation results show that the SER performance of the novel SM scheme could be improved greatly comparing with the traditional SM schemes. Moreover, the new SM scheme could weaken the limitations of the total number of transmit antennas.