Global geometric properties of dS space are presented explicitly in various
coordinates. A Robertson-Walker like metric is deduced, which is convenient to
be used in study of dynamics in dS space. Singularities of wavefunctions of
massive scalar fields at boundary are demonstrated. A bulk-boundary propagator
is constructed by making use of the solutions of equations of motion. The
dS/CFT correspondence and the Strominger's mass bound is shown.Comment: latex, 14 pages and 3 figure