The present invention discloses a power supply unit and a power supply switching method for mobile terminals. The terminal power supply unit comprises a battery, a power supply conversion module, a charging management module and a power supply switching module; the charging management module and the power supply switching module both comprise a power supply input port used for connection with an external power supply; the charging management module is connected with the battery and used for charging the battery when an external power supply is connected; the power supply conversion module is connected with the power supply switching module and used for converting the voltage of an external power supply into a power supply voltage required by the terminal and controlling an on-off state of the power supply switching module such that the power supply switching module is in an on state when no external power supply is connected, the battery supplies power to the terminal, and such that the power supply switching module is off and the power supply conversion module outputs the power supply voltage when an external power supply is connected. The present invention realizes that when the terminal is connected with an external power supply, the external power supply supplies power to the terminal and the battery is only charged without supplying power to the terminal, which is suitable for power supply switching of existing handsets and 3G handsets.