We derive the Holstein-Primakoff oscillator realization on the coadjoi
nt orbits of the SU(N + 1) and SU(1, N) group by treating the coadjoin
t orbits as a constrained system and performing the symplectic reducti
on. By using the action-angle variables transformations, we transform
the original variables into Darboux variables. The Holstein-Primakoff
expressions emerge after quantization in a canonical manner with a sui
table normal ordering. The corresponding Dyson realizations are also o
btained and some related issues are discussed.