The purpose of this study is to analyze the system of radicals of Xiruermuzi<<西儒耳目資>>(1626) written by Nicolas Trigault who was a missionary to China during the Ming Dynasty. Xiruermuzi is too famous for its phonetic annotation to be noted for its system of radicals. But this book has created its own system of radicals, which is optimized for searching characters more easily and faster. Chinese characters could be entirely new to the eyes of the Western world. Westerners had to face challenges in understanding these new characters. Xiruermuzi is the outcome after much consideration on this issue. This study could provide a background for the intelligent study how Westerners have thought of Chinese characters.