The invention provides a transformer adding decision making method based on a genetic algorithm. The decision making method comprises the steps that electric capacity parameters are acquired; theoretical total capacity of newly-added transformers is determined according to the electric capacity parameters; an objective function is constructed, the theoretical total capacity of the newly-added transformers is used as a constraint condition, and the objective is minimum cost expenditure; and the genetic algorithm is utilized to obtain the number of the newly-added transformers and the capacity of each transformer through optimization solution. Through the method, the number and capacity of the newly-added transformers can be obtained quickly and effectively, power demands of power consumers are guaranteed, and minimum cost of the newly-added transformers is guaranteed; and meanwhile, it is guaranteed that the newly-added transformers work stably, are not overloaded and run safely, reactive loss of a power grid is lowered, and the working efficiency of the transformers is improved.