The polymerization of carbon monoxide on Pt55 cluster has been studied using density functional theory. Firstly, some randomly generated oxocarbons, ranging from C2 species to C9 species, are obtained on the Pt cluster at high CO coverage. The high stability of those adsorbed oxocarbons is demonstrated by ab initio molecular dynamics simulations, and the high CO coverage can hinder the decomposition of oxocarbons especially for C2O2. By comparing the favorite structures of C4O4, C5O5 and C6O6 before and after adsorbed on the Pt cluster, it is found that all the oxocarbons preferred to be linear rather than cyclic or lactone‐like when adsorbed on the Pt cluster because of the stronger interaction between linear oxocarbons and Pt surface. Several different mechanisms of oxocarbon growth are also investigated, and we find that small oxocarbons prefer to couple with co‐adsorbed CO to form larger oxocarbons with overcoming an energy barrier of ∼ 1 eV. The high stability and low energy barrier of oxocarbon growth indicate the utilization of Pt cluster can significantly overcome the drawbacks of CO polymerization in diamond anvil cell: extreme condition and very low yield.