A spatial modulation (SM) scheme based on multi-strata space-time coding (MSSTC), called MSSTC-SM, is proposed. We allow two layers of MSSTC to be assigned unequal transmit power and phase, and codebooks composing the code set of MSSTC-SM to be assigned different rotation angles. Power and phase allocation as well as rotation angles are jointly optimized by differential evolution algorithm to maximize the minimum coding gain distance of the resultant MSSTC-SM. It is observed that the proposed MSSTC-SM outperforms other conventional transmission schemes in view of spectral efficiency and bit error probability with a comparable or lower detection complexity.