On a hot summer day, Xiao Ming saw the things around him shaking through the air above the asphalt road. Please help explain.

This is because the weather is hot, and the ground radiates the heat of the sun, so that the air above the ground becomes less dense due to heating. The closer to the ground, the smaller the density, and the farther away from the ground, the greater the density, so the air density near the ground is different, which affects vision. This is similar to the principle of seeing stars twinkling.