The invention discloses a power grid regulation and control method and system for restraining low frequency oscillation. The method includes the steps that a state variable of a single-machine infinite bus system is acquired; the acquired state variable, a preset first weighting matrix, a preset second weighting matrix, a system state matrix and a system control matrix are converted into a transformation matrix through the following formula, wherein the system state matrix and the system control matrix correspond to the single-machine infinite bus system; the transformation matrix, the second weighting matrix and the state variable are converted into an optimum controlled variable; the optimum controlled variable is used as a feedback controlled variable to conduct feedback regulation and control over an infinite power grid. By the adoption of the method and system, the restraining efficiency of low frequency oscillation is improved, meanwhile, abrasion to power grid equipment can be lowered, so that optimum control is achieved, and the stability of an electric power system and the security of a generator set are effectively improved.