This paper investigates the thematic types and derivations of subjects in Mandarin bei-passives. Based on an examination of the categorial status of bei discussed in the literature, we try a new approach by adopting Liu and Huang's [5] view that the mechanism of deriving bei-passives is argument raising (in which bei is a semi-lexical verb heading the Voice projection), and propose a simplified and unified account of bei-passives' Experiencer and Possessor subjects, as well as their typical Patient subjects. Specifically, we propose that the high applicative gei proposed in Hsu and Qu [7] can account structurally for the source of the Experiencer in bei-passives. We then present how the structure proposed in this paper accounts for Possessor related subjects in bei-passives, and explain the interpretations and the possible derivation of an extra implicit affected subject in bei-passives.