The invention discloses a method for constructing a growth and evolution model of a two-voltage-level power grid. The method comprises the steps of: simulating annual load increase and power injectionof a superior power grid transformer substation; judging whether to expand the superior power grid transformer substation according to an average capacity-load ratio of a superior power grid; determining whether a new subordinate power grid transformer substation needs to be constructed at present day, if so, determining a position, load and capacity of the new transformer substation, and accessing the new transformer substation to a power grid according to a space-time evolution model; judging a system is in power shortage, and if so, determining a new superior power grid transformer substation or subordinate power grid transformer substation according to a probability; performing N-1 verification on lines, and upgrading and transforming weak lines not satisfying the verification; and repeating the above steps until a number of iteration days exceeds a number of required iteration days. The method is designed for the power grid with two voltage levels, considers the new construction,expansion, upgrading and transforming of transformer substations, power plants and lines in the growth and evolution processes of the power grid, evolves the power grid from the aspects of time and space, and is of a certain guiding significance to power grid planning and construction.