The invention relates to a method for determining the electricity-saving quantity obtained from replacement of an air-conditioning unit by a fresh air conditioner. The method comprises the following steps: on a testing day, carrying out actual measurement under the outdoor air dry-bulb temperature condition to obtain the electricity consumption of the fresh air conditioner; carrying out analog computation to obtain the theoretical electricity consumption of the air-conditioning unit at the same outdoor air dry-bulb temperature; and subtracting the electricity consumption of the fresh air conditioner from the theoretical electricity consumption of the air-conditioning unit to obtain the project electricity-saving quantity. The method provided by the invention is capable of determining the theoretical power consumption and the theoretical running time of the air-conditioning unit under the condition that the same cooling capacity is provided for an indoor room as the fresh air conditioner, determining the computation of the electricity consumption before project reconstruction, and determining the project electricity-saving quantity. By adoption of the method provided by the invention, an energy-saving quantity determination method based on the energy-saving technology is provided for users, energy-saving service companies and energy-saving quantity audit organizations, the energy-saving effect of an energy-saving project is scientifically quantified, and the application of the energy-saving technology is further promoted.