Abstract: The power grid, whose development has drawn great attention, is serving as an essential infrastructure in the modern society and a hub of the Energy Internet. A method for evaluating the nature and mechanism of the power grid scale development from the perspective of system theory helps determine the evolution path of the power system more scientifically and accurately.Therefore, a research method for the evolution law of the power grid scale is proposed based on allometric scaling laws. The paper first introduces allometric scaling laws suitable for different complex networks, and explains that power system conforms to key elements of researching by allometric scaling laws. Then the development and evolution of the power grid is analyzed based on the theoretical analysis by allometric scaling laws. After collecting massive data for power grid models from online database of public grid models and analyzing the collected data, it can be verified that the evolution of the power grid scale comforms to allometric scaling laws and shows sublinear increase. This means that when the construction of power grid reaches a certain stage, much attention should be paid to the endogenous growth of the power grid for healthier development, instead of expanding its scale endlessly.