The mechanism of the synthesis of platinum carbonyl clusters [Pt_3(CO)_6]~(2-)_n(n=3,4) in cages of NaY was studied by IR, EXAFS ~(13)CO exchange reaction and No interaction. The results suggest that oaldized Pt species in NaY cages reacts with CO at 300-373 K to form PtO(CO) (σ_(CO)=2110 cm~(-1)) which aggregates into "Pt_3(CO)_6"(σ_(CO)=2112, 1896 and 1841 cm~(-1)) and eventually converts into dark-green carbonyl cluster [Pt_(12)(CO)_(24)]~(2-). The carbonyl "Pt_3(CO)_6" can exchange with ~(13)CO very quickly at 298 K but the exchange reaction between ~(13)CO and intrazeolite Pt carbonyl clusters [Pt_3(CO)_6]~(2-)_n (n=3,4) proceeds slowly even at enhanced temperature such as 343 K. It is interesting to find that NO breaks successively the intra and inter-tri nal Pt-Pt bonds of the Pt_(12) carbonyl clusters (even at 298 K) and the "Pt_3(C)_6" formed is further reacted to give PtO(CO) with the formation of N_2O and CO_2 in the gas phase. Pt_(12)(CO)_(24)]~(2-) can be reversibly regenerated from the Pt subcarbonyls such as PtO(CO) and "Pt_3(CO)_6" inside NaY by reacting wich CO at 300—353 K.