Abstract: The Weather Research and Forecasting model coupled with chemistry (WRF-Chem) has been used to investigate the redistribution of pollutant gas CO in two deep convective systems occurred over the Yangtze River Delta on July 27 and August 24 2014, respectively. Compared with observed radar echo properties of the convection, the onset of the convection and echo intensity simulated by WRF-Chem are consistent with observations. Both the convective available potential energy and vertical wind shear between altitudes of 0 and 6 km were larger in the case of July 27 than in the case of August 24, which led to the more unstable convective system that reached higher altitude on August 24. The analysis of vertical cross sections of CO concentration and vertical mass fluxes shows that the deep convection on July 27 could transport CO to the altitude up to 14 km, whereas CO could reach up to 16 km in the case of August 24. The differences between mean profiles of CO concentration and vertical flux divergence suggested that most of the CO was transported to the altitude of about2 km, which resulted in a higher CO concentration at the middle troposphere for the case of July 27; CO was mainly transported to the altitude of 15 km for the case of August 24, which led to higher CO concentration at the upper troposphere. Analysis of vertical flux shows that deep convective transport per hour in the case of August 24 was 1.3 times greater than that in the case of 27 July. As the deep convection lasted longer in 24 August, more CO was transported in this case than in the case of July 27.