The invention provides a method and a system for controlling a battery energy storage power station of supporting black start of a light-preserved power generation system. The method comprises steps of obtaining power station data including power grid operation states, load types, photovoltaic output values, load power values and energy storage current transformer charged states; determining whether or not a power grid has a fault according to the power grid operation state; when the power grid has a fault, calculating the number of energy storage current transformers for charge-discharge power distribution according to the photovoltaic output values and load power values and using the current transformer power optimization principle; and establishing a light-preserved combined power generation output optimal objective function, and determining the power of each energy storage current transformer for charge-discharge power distribution according to the load power values, the photovoltaic output values and the charged states of the energy storage current transformers for charge-discharge power distribution. The invention achieves black start of a power grid through a battery energy storage system combined with a photovoltaic electric field when the power grid has a fault, and achieves control of stable operation of the power grid.