This article examines the nature of Conventional-Nuclear Integration (CNI), which emerged to enhance the reliability of extended deterrence based on the ROK-US alliance in a situation that North Korea's nuclear threat has become more sophisticated, and suggests the development of the R.O.K military air & space force for the implementation of the CNI. In order to examine the nature of Conventional-Nuclear Integration(CNI), this article analyzes the North Korea's nuclear threat and the contents of the ROK-US consultations that led to the concept of Conventional-Nuclear Integration(CNI) appearing on the Korean Peninsula. In addition, it considers the implications for the R.O.K military of the concept of nuclear operation appearing in US strategy planning documents and nuclear operational doctrines, and the concept of Conventional-Nuclear integration(CNI). Based on this, the directions for development of the R.O.K military air & space force include follows; securing Dual Capability Aircraft (DCA), establishing the command structure to perform Conventional-Nuclear integration( CNI), and evolving the air & space operations plan and Multi-Domain Tasking Order(MDTO).