The expraseion of radiation pressures Produced by monochromatic red shifted diffuse light is of agained by solving the two-level atom model. The effect of the radiation pressures on atomic vefLocity distribution is calculated and their characters of monochrornatic velocity atoms are discussed The result shows that not only nearly all atoms are cooled by means of this radiation pressure, but also can be obtained monochromatic velocity atomic beam with Δv equal to 8 m/s can be obtained.