A light-emitting diode (LED) tube is applied to a lamp holder with a ballast, and has a lighting module, a first control module and a second control module connected to two ends of the lighting module, and a harmonic elimination module connected to the first and second control modules and parallelly connected to the lighting module. Each of the first control module and the second control module has a simulation circuit unit and a rectification unit. Each of the simulation circuit units and the harmonic elimination module has a switching element. The first and second control modules adjust electrical signals from the ballast, and the harmonic elimination module eliminates harmonic waves generated by the ballast so that the lighting module is compatible with the ballast and is lit. Accordingly, the LED tube can be directly mounted on a fluorescent lamp holder with the lamp holder intact.