[en] In order to give the uncertainty of activity concentration of radio xenon which leaked into air after nuclear fission happened, it was supposed that the radio xenon leakage was instantaneous, and the radio xenon leaked into a confined space, the distribution was uniform. After decay correction and in principle that the theoretical value of the average activity is consistent with the measuring values, the mathematical model of the airborne radio xenon monitoring was derived. By analyzing the sources of uncertainty, the uncertainty components evaluation, synthesis, and the mathematics model was evaluated under the certain condition. In the sources of uncertainty, radio xenon peak net count rate and efficiency value are the main sources, the concentration, volume of xenon in air and gamma-ray emission rate of radio xenon are smaller, the decay constant and time measurement are the least. (authors)