The invention discloses a light emitting device and a driving method thereof. The light emitting device comprises a plurality of light emitting diode units and a battery. The plurality of light emitting diode units are connected in series with each other. The battery is coupled to part of the plurality of light emitting diode units. When the plurality of light emitting diode units receive electricpower supplied from an external power source, an external power supply charges the battery through part of the plurality of light emitting diode units to and drives the plurality of light emitting diode units, and when the plurality of light emitting diode units do not receive electric power supplied from the external power supply, the battery discharges to drive at least one of the plurality oflight emitting diode units. An original light emitting diode unit for general lighting can be used as a light emitting diode unit for emergency lighting in emergency, thereby effectively reducing thevolume of the light emitting device and reducing the complexity of the circuit.