With　the　increasing　numbers　of　high-voltage　direct　current　transmission　(HVDC)　projects　based　on　the　modular　multilevel　converter　(MMC),　the　power　quality　of　the　grid-connected　MMC　has　drawn　attention.　By　using　peripheral　filtering　equipment　to　mitigate　the　background　harmonic　effect　on　MMC　leads　to　several　numbers　of　problems,　e.g.,　high　costs,　difficulty　in　parameter　tuning,　the　resonance　problem,　etc.　Therefore,　this　paper　focuses　on　the　mitigation　of　harmonic　pollution　for　the　MMC　controller　without　filters.　Based　on　the　multi-layer　coordinate　transformation　structures,　a　novel　nested　decoupled　synchronous　reference　frame　(NDSRF)　transformation　technique　is　presented　to　attain　the　harmonics　compensation　in　the　coordinate　transformation　process.　Besides,　analyses　of　the　proposed　NDSRF　coordinate　transformation　technique,　including　harmonics　transfer　rules　and　harmonics　rejection　principles,　are　further　given　in　the　time　domain.　Furthermore,　to　reduce　the　harmonic　content　of　MMC　output　voltages　in　case　of　a　power　grid　with　serious　harmonic　pollution,　the　harmonic　resistant　MMC　controller　based　on　the　NDSRF　technique　is　proposed.　Finally,　the　simulation　results　are　demonstrated　to　validate　the　background　harmonic　suppression　function　of　the　harmonic　resistant　MMC　controller　based　on　the　NDSRF　transformation　technique.