The counterflow diffusion combustion of diluted ethanol in various containments was numerically analyzed in the purpose of getting a deep understanding of chemdynamics in a gas generator with low ethanol concentration. A virtual specie with the same thermodynamic and transport property as water but chemically inert was used to distinguish the interference between physical and chemical mechanism. Results reveal that as the concentration of ethanol decrease, the flame front, along with the disappearance of the second exothermic reaction region, tends towards the fuel side as a whole. The H₂O will exert an inhibitory effect when the concentration of ethanol is reduced to the ultimate low value.