The invention discloses a method for protecting the vehicle battery with the function of analyzing power noise signal mode and the device thereof. The device comprises: a power characteristics sensingdevice for detecting the voltages of vehicle main battery and standby battery, and detecting the current value and power noise signal; a power characteristic analysis method: analyzing the spectrum mode of the power voltage, current and noise signal by employing the power characteristics, and further judging vehicle operation status and power status; a power manage and control unit, adjusting timeinterval via variable timing circuit, and switching or cutting main battery or standby battery according to the vehicle operation and power status. The invention can prevent power exhaustion after th e engine motor stopping.