We propose and study a spin-orbit interaction based mechanism to actively cool down the torsional vibrationof a nanomechanical resonator made by semiconductor materials.We show that the spin-orbit interactions of electronscan induce a coherent coupling between the electron spins and the torsional modes of nanomechanical vibration.Thiscoupling leads to an active cooling for the torsional modes through the dynamical thermalization of the resonator by thespin ensemble. We propose and study a spin-orbit interaction based mechanism to actively cool down the torsional vibration of a nanomechanical resonator made by semiconductor materials. We show that the spin-orbit interactions of electronscan induce a coherent coupling between the electron spins and the torsional modes of nanomechanical vibration. thin coupling leads to an active cooling for the torsional modes through the dynamical thermalization of the resonator by thespin ensemble.