Reasons for the occurrence of low frequency oscillations in power system are analyzed, and the damping characteristics of asynchronized turbogenerators (ASTG) are investigated thoroughly. Based on these damping characteristics, a theory of restraining low frequency oscillation by partially replacing the traditional synchronous generator in power systems with an ASTG is proposed. A typical two machines, two area power system model is established. A simulation studying ASTG restraint of low frequency oscillation in power systems is carried out. The simulation results show that power systems incorporating an ASTG possess excellent dynamic and transient operation characteristics, and that low frequency oscillation in power systems is effectively restrained.