Oxyhydrogen (H-2/O-2) combustion with carbon dioxide (CO2) was used widely because the replacement of nitrogen (N-2) with CO2 was applied to reduce emissions of nitrogen oxide (NOx). However, the replacement of N-2 with CO2 brings about cellular premixed flames owing to intrinsic instability. This study focuses on the effects of CO2 ratio on the characteristics of cellular premixed flames on flat burner at atmospheric pressure. Oxyhydrogen flames were experimentally investigated with variation of CO2 ratio, equivalence ratio, and total gas flow rate. Then the cell size, power spectral density, and reconstructed attractor were obtained. When the CO2 ratio increased, greater cell size, lower sharp peak frequency of power spectral density, and the more complicated doughnut ring of reconstructed attractor were found. It was caused by the replacement of N-2 with CO2, which affected diffusive-thermal instability. As the equivalence ratio increased, the smaller cell size, higher sharp peak frequency, and smaller doughnut ring were obtained owing to the decrease of instability intensity. Moreover, we obtained smaller cell size, higher sharp peak frequency, and smaller doughnut ring when the total gas flow rate increased. The results showed that the increase of CO2 ratio and the decrease of equivalence ratio and total gas flow rate induced greater cell size, lower sharp peak frequency, and a more complicated attractor as higher instability intensity.