The invention relates to a method for distinguishing a transformer capacity-reducing designed product. The method comprises the steps of, firstly, finding a hottest spot of a transformer winding staying at a stable operating state by using an infrared thermal imager; secondly, measuring an actual temperature value of the hottest spot by using an infrared thermometer; thirdly, comparing the measured actual temperature value with insulation system temperature data specified in GB 1094.11 of an insulating material used by the transformer; and fourthly, judging the transformer is a capacitor-reducing designed product if the measured actual temperature value is greater than the specified insulation system temperature. The method provided by the invention solves a problem of judging whether a transformer product is the transformer capacity-reducing designed product or not under a field condition and judging whether the transformer product meets the rated capacity or not. The method is simple and reliable, and saves the acceptance time and the acceptance cost. Meanwhile, the safety of a power grid is protected, thereby laying a foundation for continuous uninterrupted power supply.