The former studies deem that semantically, PRO forms local lexical binding relation to its antecedent. And syntactically, it is the trace after the move of its antecedent. However, this semantic and syntactic interpretation to PRO fails to satisfy the requirement of interpretive adequacy. The present study first compares PRO, NP trace and other empty categories and deems that semantically, PRO spans across different event structures and is the co-argument of two event structures and syntactically, PRO follows the derivational pattern of “first spelled out then deleted”. This designation of the semantic and syntactic feature of PRO satisfies the logical match between theta role and case. The semantic and syntactic features of PRO defined by present study can be better applied to interpreting some exceptional cases of Chinese, English, Icelandic and Kirundi.