With the improvement of urbanization, the temperature of the city also changes, and the urban heat island is most closely related to the temperature change. The surface temperature in the center is higher than that in the suburbs, causing the atmosphere to rise and form a low-pressure vortex, which is not conducive to the discharge of pollutants and waste heat from exhaust gas, and will cause harm to the physical and mental health of residents over time. The purpose of this paper is the effect and urban air pollution diffusion. In the experiment, the large eddy is used to simulate the diffusion of two typical urban pollution sources. The diffusion of fixed sources and their impact on ground are affected by the atmosphere. During the day, when there is a movement in it, the pollutants from fixed sources are easier to reach the ground.