Beijing Normal Univ, Dept Phys, Beijing 100875, Peoples R China
; Acad Sinica, Inst High Energy Phys, Beijing 100039, Peoples R China
; Acad Sinica, Inst Theoret Phys, Beijing 100080, Peoples R China
The York's formalism of path-integral approach to the thermodynamics of black holes is applied to de Sitter space-time. The first law of thermodynamics for de Sitter space-time is given, which includes a "work term" with respect to the cosmological constant.