In view of an inquiry into the flow field and pollutant diffusion law of the blow-suction ventilation system under the non-isothermal parallel flow, CFD method is used for a simulation of the typical three-dimensional blow-suction ventilation system with a symmetrical arrangement on both sides. A comparison between the simulation results and the experimental data reveals that the change trend is basically consistent. The results show that when the air supply velocity in the flow field remains constant, with a temperature difference between the jet and the ambient air, the Archimedes number increases while the axial velocity decreases rapidly with an increase of the temperature difference. The axis temperature decreases along the direction of the blowing and suction flow field, whereas the vortex center shows an initially increasing and a subsequently decreasing trend. In terms of pollutant diffusion, with the air supply temperature close to the ambient temperature, the system is characterized with the strongest ability for the pollutant absorption. When there is a constant temperature difference between the jet and the environment, the air supply speed in the flow field increases, while the Archimedes number decreases; the axis temperature increases first and then decreases, while the upward shift of the vortex center in the flow field decreases. In terms of pollutant diffusion, an increase in the air supply speed is conducive to pollutant absorption in the system, thus reducing the escape of pollutants.