A method based on anemometer tower measurement data for determining the discarded wind electrical power of wind farms. On the basis of anemometer tower measurement data, the method takes into consideration the impact of such factors as terrain, topography, and wind turbine wake, calculates wind speed at wind turbine hub height, and obtains a theoretical wind turbine power according to a power curve, then adds up the theoretical power of all the wind turbines of a wind farm to obtain a total theoretical power thereof; finally, the total theoretical power of the wind farm and the actual power thereof are respectively integrated over time, to obtain a theoretical and an actual electrical power; subtracting one from the other yields the discarded wind electrical power of the wind farm, thus providing precise calculation of wind farm discarded wind electrical power. The present method is applicable to all types of wind farm and resolves problems of low accuracy in the calculation by the sample turbine method of discarded wind electrical power.