The invention relates to an internal circulation cooling air quantity optimization method of a wind power generator. The method comprises the following steps of 1, building a temperature calculation model of a wind power generator; 2, dividing the work time of the wind power generator into a plurality of limited time periods; 3, in the same time period, calculating the motor temperature at different internal circulation quantities; in the same time period, calculating the motor copper consumption under the condition of different internal circulation air quantities; 5, in the same time period, calculating the ventilation power under the condition of different internal circulation air quantities; 6, in the same time period, determining the internal circulation quantity when the consumption is minimum; 7, determining the frequency of an internal circulation wind power generator; 8, entering a next time period; repeating the calculation process from the step 3 to the step 7. The work time of the wind power generator is divided into limited time periods; the internal circulation air quantity is changed by combining the operation data of the wind power generator in different time periods; the power of the internal circulation air wind power generator is reduced.