A charging device includes a plurality of DC charging ports, a detecting circuit and a current output unit. The DC charging ports includes at least one first charging port and at least one second charging port. The output currents provided by the first charging port and the second charging port are lower than or equal to a first current limit and a second current limit, respectively. The detecting circuit is coupled to the DC charging ports to detect the output currents from the DC charging ports. When the current required by the first charging port is lower than the first current limit, the current output unit correspondingly supplies a requested current to the first charging port and distributes a surplus current to the second charging port. A total current limit of the DC charging ports is higher than a supply current limit.