Under the framework of Optimality-Theoretic syntax (OT syntax) and on the basis of the hypotheses of double shell of VP, internal generation of NP within VP as the external argument, direct numeration of the expletive there from the lexicon and NP as the presentational focus in the existential clause, the article proposes an OT analysis of the English existential clause by resorting to such constraints as ALIGN-PRES-FOCUS, CASE_nom, OB-SPEC and FULL-INT and their hierarchy. The article argues that the NP in the existential clause is internally generated as the external argument of VP, and is thus endowed with the nominative case, but ALIGN-PRES-FOCUS, a pragmatic constraint on syntax, prohibits the raising of the NP following the VP, which, as a result, causes the unmarking of its nominative case on the surface form and the violation of the constraint CASE_nom. In order to meet the condition of OB-SPEC, either the expletive there is selected from the lexicon or the locative phrase is raised to fill the position of the specifier of IP.