Abstract: This paper deals with the main syntactic properties and syntactic derivation of the surface unaccusative structure in Mandarin Chinese.The selected NP argument of unaccusative verbs originates as the internal argument in VP-complement position.Under a phase-based minimalist syntactic account,the internal NP argument in a postverbal position agrees with the finite T-probe and its unvalued uninterpretable Case feature is valued as nominative.When frozen in its base position,the NP argument serves as presentational focus or unmarked end focus and could not undergo further movement.The focalized postverbal NP argument in structures with unaccusative verbs differs substantially from the postverbal NP argument in structures with unergative verbs.More specifically,the former remains in situ in its base VP-complement position,while the latter is the result of the overt rightward movement of the external argument from spec-TP to spec-FocusP.