The invention relates to a key electricity consumption industry identification method and system. The electricity consumption statistical data of each industry in an area to be measured in the preset time period are acquired, and electricity consumption classification is performed on all the industries by using cluster analysis according to the electricity consumption statistical data of each industry so that the electricity consumption industry class to which each industry belongs is obtained; then the proportion of electricity consumption of each electricity consumption industry class is calculated according to the electricity consumption statistical data and the electricity consumption industry class, and then the size of the influence value of the electricity consumption fluctuation of each electricity consumption industry class on the total electricity consumption fluctuation is calculated according to the electricity consumption statistical data and the electricity consumption industry class; and finally whether the industry included in the electricity consumption industry class is the key electricity consumption industry is judged according to the proportion of electricity consumption of each electricity consumption industry class and the size of the influence value so as to realize accurate key electricity consumption industry identification.