English sentential subject extraposition is a marked feature, but i is quite a systematic structure. This study aims to provide an extraposition occurrence environment and a plausible trigger for the extrapositionof a sentential subject. To this end, we first identify a total of 414 examples of COCA corpus, and then discuss thier predicates as well as sentential types. An adjectival predicate (52.2%) is frequently employed without a strict semantic restriction, whereas that-clause (55.8%) and to-infinitival clause (35.5%) are mostly extraposed at the sentence-final position. From this corpus data, we suggest that the extraposition occurs across no more than the first complement of a head verb if and only if the complement is not a clause.