Using the data of patents granted by USPTO during 2013~2017 from WIPO IP Statistic Data Center, this paper examines the general trend and the main technical fields of international patents granted to Korea, China and Japan. The Patent Activity Index(PAI) was used to analyze the dynamic changes of international patents in the top 5 technical fields. The results show as follows. First, the number of international patent applications and registration by China has been increasing rapidly in recent years. Second, the technical fields of international patents granted by China and South Korea are mainly concentrated in several fields, such as computer technology, semiconductors, digital communication, audio-visual technology and electrical machinery, apparatus, energy. Third, through the PAI index analysis, the technology innovation and concentration of South Korea and China surpassed Japan in telecommunications technology field, and China’s development in the semiconductor field is the strongest. The technological innovation performance of Japan was analyzed as to be relatively higher than that of China and South Korea in the field of electrical machinery, apparatus, energy.