Abstract: Under the government target on carbon peaking and carbon neutrality, the establishment of a modern power system is an inevitable trend for renewable energy source (RES)-dominated generation to achieve low-carbon transition. However, with the large-scale RES integration, power systems are gradually developing towards the characteristics of high proportions of both RESs and power electronic converters, posing great challenges to the frequency stability of future power systems. Therefore, we provided a comprehensive and systematic investigation and outlook of modern power system inertia-frequency sensing and control technology across following three dimensions: frequency regulation resource optimization-"Cloud", inertia sensing and warning visualization-"Grid", and RES inertia emulation-"Terminal". Firstly, the necessity and technical framework of exploring system secure control and operation are described. Then, current progresses in frequency regulation resource optimization based on near real-time frequency dynamics prediction are analyzed, developments of system inertia sensing and warning visualization based on phase measurement units are discussed, and the key technologies of RES grid-forming inertia emulation control based on supercapacitor stored power are elaborated in detail. Finally, the prospects in system inertia-frequency technologies across "Cloud-Grid-Terminal" are presented.