A method and device for controlling a distributed direct current power supply system are provided in embodiments of this disclosure. The method includes: acquiring a direct current busbar current of the distributed direct current power supply system; acquiring, according to the direct current busbar current and a rated capacity of a power conversion unit in the distributed direct current power supply system, a quantity of power conversion units that meets a power requirement of a load; and adjusting, according to the quantity of power conversion units, power conversion units that are turned on in the distributed direct current power supply system. The device is used to implement the method.