The invention discloses an optimization method for improving safety and stability of grid frequency. The optimization method comprises the following steps of: determining a grid size, grid characteristics, an operation mode and a setting condition of a safety and stability control device of a target power system; determining whether the risk that the grid frequency is out of limit exists after a grid fails; implementing a measure for cutting off a pumped storage power station unit; determining a control measure for power of a speed-up or speed-down direct current line; and selecting starting frequency of the power of the speed-up or speed-down direct current line and determining speed-up or speed-down regulating quantity for power of the direct current line through simulating calculation. According to the optimization method, the frequency stability of the grid after failure is improved by using the control measure for the direct current line and a pumped storage power station, the direct current adjustable capacity and the pumped storage power station in the system can be effectively utilized, the frequency maintenance level of the system after failure is improved, the safety and stability control measures such as cut-off of a power set and load shedding are reduced, and the influence of the failure of the power system on power operation, industrial production and life of people is reduced.