North Korea intended to increase the power of its nuclear weapons and standardize warhead to be loaded in ballistic missiles through the 4th and 5th nuclear tests. In this study, three kinds of nuclear weapons that North Korea might have used in the 4th and 5th nuclear tests to achieve their technical goals were suggested. Monte Carlo modeling and various technical assessments have shown that boosted fission weapons are most likely to be used. Also, using the empirical formula considering the burial depth of explosion, we found that the yield of the 4th and 5th nuclear tests is at least twice as strong as that is expected it could be and the initial design power could reach 8kt before amplification. This means that North Korea has already achieved a substantial level of nuclear fusion technology through the 4th test and has made a breakthrough in the miniaturization of nuclear weapons through the 5th test. After two or three additional tests, North Korea is expected to have nuclear missiles equipped with nuclear warhead by 2020, which is expected to complete ballistic missile development.