The selective catalytic reduction of nitric oxide by methane was studied over CaO catalyst in a bubbling fluidized bed in the temperature range of 800-900 ℃, in which NO cannot be reduced by CH4 without CaO catalyst. The nitric oxide conversion was found to depend on oxygen and CH4 feed concentration, and also on temperature. In addition, the presence of water vapors in the flue gas enhanced the NO reduction admirably well in the absence of O2. But water vapor has an inhibiting effect on the reaction while O2 is present in the flue gas. The addition of CO2 poisoned the CaO catalyst and exhibited a detrimental effect on NO conversion at the working temperature range, 800-900 ℃. However, with a temperature rise to 900 ℃ the CO2 poisoning effect on NO reduction was weakened. The mechanism was studied and discussed according to the references in the paper.