The method to analyze non-methane hydrocarbons( NMHCs) by gas chromatography with two valves,two columns and single FID detector is established. By measuring total hydrocarbon and methane directly,the NMHCs can be calculated. The high boiling-point components are reverse-flowed out the methane column,which avoid analysis interference from high boiling-point components. The results show that this method is reliable. The total analysis time is less than 1 min,the linear correlation coefficient of standard cur...