Abstract: The resistive beam loading in a travelling wave structure is well known for the case when bunches travel on the crest and reduce the fundamental mode electric field. This type of beam loading could be compensated by increasing RF feed power. Generally, bunches could travel on each phase and in a special case travel on zero-crossing and it is not enough just to change the RF feed power to compensate beam-induced fields. General beam loading compensation is well-known for a single cell cavity by changing the RF feed power and detuning the structure. In this lecture, the concept of detuning in a TW structure will be shown and the evolution of beam-induced fundamental mode electric field will be derived and finally, it will be shown how to compensate beam loading by changing the phase velocity in comparison to bunch velocity.