The invention provides a wind turbine generator system yaw system control performance optimization method and system. The method comprises the steps of acquiring the data of incoming flow air in front of a machine cabin at fixed time intervals, wherein the data of incoming flow air includes the incoming flow air speed, the incoming flow absolute wind direction and the wind direction of incoming flow relative to the machine cabin; sectoring the incoming flow absolute wind direction according to the preset angle intervals, and sectioning the incoming flow air speed according to the preset wind speed intervals; carrying out the first time of grouping on the data of the incoming flow air according to sectors and subsections; calculating the yaw errors of the corresponding groups according to the wind direction of the incoming flow relative to the machine cabin to obtain a yaw error optimization model; and when the yaw system is optimized, inputting the measured incoming flow air speed and the measured incoming flow absolute wind direction into the yaw error optimization model, carry outing matching to find the corresponding yaw error, and correcting the corresponding yaw error to the input of a yaw control system. With the wind turbine generator system yaw system control performance optimization method and system, different optimizing strategies can be adopted for wind turbine generator systems of different models in the situations with different wind speeds of incoming flow, and the optimizing accuracy of yaw errors is improved.