It has become a common practice to connect the gas distribution system with various gas sources. However, constituent difference of natural gas may have negative effectgs on the end users. To understand the influence of different gas constituents on the CO emission of gas cooker and avoid the damage to the indoor air quality of a large number of end-users, an experimental study on the CO emissions of gas cooker was carried out. First, the distribution of 12T natural gas constituent in China was investigated, and six groups of the original natural gas and the corresponding three-component gas were prepared by using the principle of equal Wobbe number and the conservation of hydrocarbon atom number. The CO emission of the gas cooker under each set was also tested. Then the difference between be CO emission of the original natural gas and that of the three-component gas was discussed. Different three-component gases based on Wobbe number and PN number were tested on the cooker. Results show that the CO emission of the three-component gas was equivalent to that of the original natural gas. The gas quality parameters, Wobbe number, and PN number could be used to describe the variation of CO emission of gas cookers with different gas constituents. A series of CO isoline were revealed on the PN-W diagram, which can be used to predict the CO emission of gas cooker with different gas constituents. A method to establish the CO emission limit was put forward based on the diagram. The work of this paper is of practical significance and value for ensurance indoor air quality and gas source quality management of distribution network.