The invention relates to a safe start-up margin calculation method and a start-up method based on power grid frequency stability. The following technical scheme is used by aiming at the deficiency that there is no power grid safe start-up margin calculation method in the prior art. The safe start-up margin calculation method based on the power grid frequency stability comprises the following steps: S1, obtaining the total power grid-connected installed power, the maximum missing power and the minimum power grid frequency only under the condition of primary frequency modulation; S2, obtaining the power grid frequency stability according to the total power grid-connected installed power, the maximum missing power and the minimum power grid frequency; S3, obtaining the theoretical start-up power required under a specific missing power and a specific power grid accident frequency according to the power grid frequency stability; and S4, subtracting the theoretical start-up power from the total grid-connected installed power within the period so as to obtain the safe start-up margin. The calculation of the start-up margin under the safe power grid frequency can be simply and effectivelyrealized.