Flexible hard coatings with high density, high surface integrity and smooth surface morphology exhibit simultaneously high hardness, high toughness and high crack resistance which represent a new class of high-performance coatings. However, their depositions are a hard work. Deep oscillation magnetron sputtering (DOMS) is a novel high-power impulse magnetron sputtering, which become a hotspot in tribological hard coatings around world. Using a series of modulated micro-pulse of voltage oscillation, DOMS can achieve virtually arc-free high-power discharge to generate highly ionized target species to obtain high dense plasma with low ion energy and high ion flux. These features allow to prepare high-performance nanostructured coating, which can be modulated by composition, structure and properties using a series of micro-pulse under optimized deposition conditions. In this paper, we summarize characteristics of flexible hard nanostructured coatings and research progress in recent years of flexible hard nanostructured coatings deposited by DOMS technology.