A power warning system comprises a first detection module, a second detection module, a warning module and a power module; wherein, the first detection module is electrically connected with a power button of electrical equipment and is used for detecting whether the power button of the electrical equipment is pressed down; the second detection module is electrically connected with the first detection module and a power supply of the electrical equipment and is used for detecting whether the power supply of the electrical equipment is live; the warning module is electrically connected with the second detection module and is used for sending out warning signals when the power supply is dead; the power module is simultaneously connected with the first detection module, the second detection module, the warning module and the power supply electrically and is used for supplying power for the first detection module, the second detection module and the warning module; when power lines are well connected, the power supply charges the power module. In addition, the invention also provides a power warning method.