Two thousand and four or five hundred years ago,in a Chinese classical book,The Etiquettes of the Zhou Dynasty,optical phenomena were first classified into tengroups according to their nature,presenting the world’s earliest detailed optical classification system. The meanings defined. however,have been ambinguous and vague in the last two thousand years or so. This paper compares the definitions given by five famous authorities in history,proposes three principles for distinguishing true definitions from wrong ones,and hence reconstructs the original definitions of the pre-Qin’s ten natural optical phenomena in the earliest optical system. Finally,evaluation is made of the observation method and the original definitions in the optical classification system.