Abstract: The method for NOx analysis in the recyclable olefin refinery gas was established. The solid absorption tube for pre-concentrating NO2 from gas sample and the special tube for NO oxidation to NO2 were prepared. The simulating gas containing trace NOx was prepared by the dynamic distribution equipment and used as an evaluation gas. Based on the quantitative parameters of the method and the interference of coexisting component determined by us of ion chromatography(IC) technique, a complete analytical method for NOx, consisting of pre-concentration solid absorption tube on-line and ion chromatography detection , was developed. The limits of determination for NO2 and NO of gas sample are 2 nL/L and 3 nL/L, respectively, when the sampl gas is 25 L. The analytical method of NOx can be well applied to determine the contents of NO2 and NO in the gas samples from dry gas concentration of ethylene cracking unit and steam cracking unit of Yanshan refinery.