In order to analyze and suppress the reference voltage fluctuation of the analog-digital-converter(ADC) in methane detection,the expression between methane concentration and voltage fluctuation is derived,and the effect of the fluctuation on ADC′s practical resolution is calculated.To decrease the noise level,a three-stage voltage regulator is specially fabricated,and the average voltage fluctuation drops from 2 mV to 0.6 mV.Considering that the voltage fluctuation is unavoidable,the converted digital numbers corresponding to different analogue voltages are overlapped and the detection characteristics cannot be precisely determined,a novel noise suppression method based on the second-quantification principle is proposed.Under different noise levels,the detection stability,accuracy,sensitivity and detection limit are experimentally studied.The results show that when the average voltage-fluctuation decreases from 2 mV to 0.6 mV,the detection accuracy is improved from 12.9% to 5%,the detection limit is decreased from 26×10-6 to 20×10-6,and the sensitivity under the detection limit is enhanced from 30×10-6to 20×10-6.The proposed novel second-quantification-suppressing method is experimentally reasonable,which can also be adopted in the detection of other gases with similar mechanism.