After Kim Jong-un came to power, North Korea went beyond the nuclear weapons research and development stage to complete its nuclear force and become a nuclear power. It is a trend to expand and develop its nuclear strategy while requesting status and partially referencing and imitating the nuclear operation strategies of existing nuclear powers. The purpose of this study is to approach the reality of North Korea's nuclear strategy after Kim Jong-un took power and analyze its implications to help establish and respond to Republic of Korea's security and defense and military strategies. To this end, we systematically analyze factors affecting the formation of a nuclear strategy, such as North Korea's nuclear and missile capabilities, North Korea's political system, the claims and remarks of the supreme leader and government agencies, nuclear-related constitutional and legal system, and military strategy. North Korea's nuclear strategy can be said to have expanded from an existential and minimal deterrence strategy to a limited deterrence strategy in terms of a nuclear deterrence strategy. In terms of nuclear doctrine, it also has the character of a retaliatory deterrence strategy with a certain level of retaliatory capability from a denial deterrence strategy. In terms of nuclear posture, from catalytic posture in the early stage of nuclear development, it now has a mixed type of assured retaliation posture and asymmetric escalation posture. In addition, North Korea is evolving and expanding its nuclear strategy by combining tactical nuclear weapons with conventional forces and declaring the most offensive first strike strategy.