In order to solve the problem of checking the conversion efficiency of the conversion furnace of the nitrogen oxide (NOx) analyzer, a quantitative analysis of the existing calculation model of the conversion efficiency of nitrogen oxides was carried out, and combined with the meaning of errors in the measurement work,two concepts of nitrogen dioxide conversion error and nitric oxide detection error during the detection process of nitrogen oxide analyzer were defined. The principle of non-spectroscopy infrared method detection of nitrogen oxide analyzer and the necessity of conversion efficiency check are introduced. The conversion efficiency of nitrogen oxide analyzer is checked using an ozone generator. A second-order calculation model of conversion efficiency based on the conversion error of nitrogen dioxide and the detection error of nitric oxide is proposed, and the principle of stepwise regression is used to determine the independent variables in the model and estimate the parameters. The research results show that, compared with the calculation model embedded in the nitrogen oxide analyzer and the first-order calculation model, the degree of multiple coefficient of determination of the fitting equation close to 1 increased by 96.8% and 51.5% on average, and the residual sum of squares decreased by 85.1% and 31.7% on average, so that the nitrogen oxide analyzer can more accurately and reliably detect the concentration of nitrogen oxide in the exhaust gas of the vehicle.