The invention relates to an automatic air-fuel ratio control method for realizing power maximization of a gas generator set. The air-fuel ratio of the gas generator set is controlled by taking realization of power maximization of the gas generator set as a control basis. After the gas generator set is connected to a power grid, a corresponding relationship exists between power and the air-fuel ratio under the condition that the open degree of a throttle valve of a speed regulator is not changed, namely the total air inflow is not changed, a power/ air-fuel ratio curve is formulated, the curve has just only one extreme point which is extreme power, the extreme power corresponds to a perfect air-fuel ratio, the power is reduced along with increasing of difference between the air-fuel ratio and the perfect value, and even reverse power appears. According to the corresponding relationship, the method is designed. The automatic air-fuel ratio control method for realizing power maximization of the gas generator set overcomes shortcomings in the prior art, and is wide in applicability, high in reliability and high in response speed.