The evaluation of large-scale science popularization activity is a significant way to evaluate the effect of the science popularization activities. The organizers, playing the important role in the whole implementation process, are the essential objects of science popularization activity evaluation. The significance, objective and method of the evaluation are discussed in this paper, which is based on the case of the evaluation of the participant organizations of 2012 Beijing Science Festival. The main results of evaluation are illustrated and their significance to the science popularization activity is explained.