The invention provides a tandem connection type charging device and a charging method thereof. The tandem connection type charging device comprises a power supply input end, a power supply output end, a charging control unit and a power supply detection unit, wherein the power supply input end is used for receiving input power, one end of the power supply output end is connected to the power supply input end while the other end of the power supply output end is connected with another tandem connection type charging device so as to supply subordinate power supply, the charging control unit is connected with the power supply input end and the power supply output end and is used for storing an input power upper limit value, obtaining output power by current division of the input power, generating charging power according to the output power and charging a battery, and the power supply detection unit is connected between the power supply input end and the power supply output end and is used for measuring supplying power of the input power, when the power supply output end is connected with another tandem connection type charging device, the battery of the second tandem connection type charging device is charged at first, and the residual power is distributed to other tandem connection type charging devices.