For the multiphase motor drive system, current harmonic components in stator windings and the common-mode voltage are the main factors affecting the control performance. In this paper, a novel model predictive torque control (MPTC) considering both harmonic and common-mode voltage suppression is proposed to improve the control performance. First, with the vector space decoupling (VSD) theory, 12 virtual voltage vectors are constructed based on the principle that the amplitudes of the vectors in the x-y harmonic subplace are zero to achieve the harmonic suppression. Then, these 12 virtual vectors are further simplified to six vectors to realize the common-mode voltage suppression, and they are taken as the candidate vectors to be rolling optimized to output the optimal voltage vector. This novel MPTC strategy can reduce the computational burden and avoid the weight factor design for the traditional multi-objective optimization. The effectiveness of this novel MPTC strategy was verified by simulations and experiments in comparison with normal MPTC methods, and it can save over 44% of the execution time of the traditional MPTC method and provide better suppression of the harmonic current components and the common-mode voltage.