In this article I inquired into the meanings of 'chance(机會)' and 'occasion(机遇)' in three aspects. The two words are synonyms which have a nominal property, being consisted of a noun plus a verb. First, I analysed lexical meanings and meaning systems of the two words, and found out morphemic characteristics of 机(j?), 會(hui), and 遇(yu)? included in the two words. Second, I deducted the intrinsic elements of the two words, which are ambiguous and similar, but have different meanings according to the contexts, through their daily usages. From this deduction I introduced what makes the ambiguity and difference of their meanings by categorization and conceptualization theory, and clarified their differences in the sameness, and their sameness in the differences. Lastly, I examined the categorized meaning structures of the two words through their daily usages in modern chinese and ancient chinese, respectively. My findings are (1) Categorized fields of the two words in modern & ancient chinese show similar aspects, while their meaning fields show a great difference. (2) In modern chinese 'chance' is used in almost all social fields, while 'occasion' is mainly used in the fields of economy and trade, natural sciences. (3) In modern & ancient chinese the 'chance' is more frequently used than the 'occasion', and more diversely in categorized meaning fields.