The invention relates to a free generation control method for a wind farm of an electric system in consideration of grid security, and belongs to the technical field of the operation and control of a new energy accessed power system. According to the principle of minimal abandoned wind and fair-share scheduling, when a wind power generation accepting space of a power grid is distributed to all wind farms according to a method of a minimal wind power generation load deviation, in the free generation state, one the one hand, the unnecessary abandoned wind of the wind farm can be prevented due to a small active set value, and the greater active set value can be prevented, therefore, the active capacity of the wind farm can exceed the bearing limit of a power grid. The method can be integrated in a wind power generation active control master station system operated by a control center, therefore, the system can implement an optimum control strategy according to a wind power generation operating state and the operating state of the power grid, and ensure the power grid to have enough underspin safe space; furthermore, the safe active power of a section of a connecting circuit between the wind farm and the power grid can be realized, and the fair-share scheduling among all wind farms can be considered.