A constant-power electronic cigarette protecting against dry-heating and a controlling method thereof are provided. The electronic cigarette comprises a vaporization rod (1) with a heating resistor arranged therein and comprises a battery rod (2) in which a battery (4), a control circuit board (5) and an unlock switch button (6) and a starting switch are arranged. The heating resistor is a variable resistor with a resistance variable depending on a change in temperature and having a positive temperature coefficient. The control circuit board (5) is arranged with a microcontroller chip, a resistance detection unit, a constant-power output control unit, an output feedback unit, wherein the unlock switch button and the starting switch are electrically connected with the microcontroller chip.