The invention discloses an optimized dispatching method and a system for reducing smog in a power network. The method comprises the following steps: according to the current operation mode of the power network and the start-stop state of a thermal power station, the smog degree index of the whole country in each day in the future period is estimated; when the haze index exceeds the threshold valuein any future day, the optimal dispatching model of power grid haze reduction is used to dispatch the power grid haze reduction; the optimal solution of the optimal dispatching model for smog reduction in power network is obtained; the on-off state of the generator corresponding to the optimal solution is taken as the optimal dispatching scheme for smog reduction. According to the current smog level and the start-up and shut-down state of the thermal power station, the invention can formulate an optimized power network smog reduction dispatching scheme, effectively reduce the smog level, andhas important guiding significance for large-scale smog prevention and control.