The invention discloses a lamp tube detection method and a device thereof which are used for detecting the internal voltage of a lamp tube which is internally encapsulated by gas; whether the internal voltage of the lamp tube to be detected exceeds the requirement of the specification or not is judged by the difference of lighting duration of lamp tubes to be detected with different internal voltages and lamp tubes with standard internal voltages under the same driving voltage. The detection method and the device can avoid the damage test for detecting the internal voltage of the cold cathodefluorescent lamp tube, ensure that all lamp tubes can be detected and greatly improve the detection and selection efficiency of the lamp tubes.