Single-scattering diffuse backscattering Mueller matrices expressions based on Stokes vectors of the backscattered light are derived when a narrow pencillike beam is perpendicular to the surface of the plane of turbid medium. Using Mie theory of light scattering, the characteristic distribution pattern of single-scattering Mueller matrices, and the correlation with particle number density and particle diameter are discussed. The results indicate that the azimuthal variations gradually disappear when the particle number density increases, and m22, m33, m23, m32 elements are the more pronounced azimuthal variation characteristic. For azimuthal angle =45°, m22 and m33 decrease with increasing particle size if particle size parameter is smaller than the characteristic parameter, otherwise, m22 and m33fluctuate and gradually increase. And when the particle size and particle number density are varied, all of the Mueller matrices elements intensity patterns' dependence on the radial are the same, exponential, decaying, for any azimuth angle.