The formation mechanism of linear-carbon-chain molecules, CnO (n = 2 -9), synthesized in the discharge Of C3O2 has been investigated on the basis of detailed analyses of previously obtained FTMW spectroscopic data. The relative abundances of the CnO products determined from their rotational spectrum intensities agree with those for the CnO(+) ions. The active chemicals in the reaction system include :C and :CCO only, and the observed products exclusively consist of CnO, leading to a likely formation mechanism of the atomic-carbon addition and ring opening reaction. This formation mechanism is simple and efficient, and it is applicable not only to linear-carbon-chains but also to a wide range of carbon processes, in particular, to ultra low temperature or incomplete combustion conditions.