The invention discloses a frequency converting control method and system of a condensate pump of a condensed steam generator set. When a frequency converter is in a liquid control mode, the water level of a deaerator is controlled by the frequency converter and a water adjusting valve on the deaerator, and the frequency converter controls the water level of the deaerator by adjusting the rotating speed. A water feeding main adjusting valve on the deaerator is maintained at certain aperture according to the load of a machine unit; and under the same load, when the machine unit is in a load up stage, the aperture of the water feeding main adjusting valve is maintained to be small, and when the machine unit is in a load down stage, the aperture of the water feeding main adjusting valve is maintained to be large. Simultaneously certain load space can be generated by control of two clamped curves during load up and load down, and frequent aperture changing of the water feeding adjusting valve caused by small load fluctuation can be avoided. The rotating speed of the frequency converter can be lower, the current is small, the output frequency of the frequency converter is in the adjustable and economical range, and energy consumption of the frequency converter is reduced.