Abstract: This paper discusses the investigation on the effect of reactive activity of quadruply promoted ammonia synthesis catalyst A110 by using synthesis gas containing <5-~30ppm water vapor under high pressure. The experimental data were treated with the modified T- equation. We have found that the poisoning factor POIS=k/kTO is approximately in inverse proportion to VH2O and proportional to 6th power of absolute temperature, and minimal relation with pressure. The catalysts appeared to be inflicted by poison when water vapor reached PH2O/PH2 =10×10-6. The intrinsic apparent energy of activation raised from 38000 kcal/kg-mol to 40000 kcal/kg-mol or higher as the amounts of water vapor poisons increased. In comparison with the catalysts original intrinsic activities, appreciable change of kinetic performance under poisoning conditions, especially in the lower temperature region, has been acquired. After 15 days repeated poisoning experiments it is discovered that most of the catalytic activity has been recovered but a certain degree of its activity has been permanently destroyed by poison. Calculation of the empirical correlations of the poisoning factor of trace water vapor has been procured.