Based on the extended Huygens-Fresnel principle and theory for the turbulence, the analytical expression for the beam propagation factor (M2-factor) of partially coherent beams propagating in a turbulent atmosphere has been derived. The effects of the structure constant of the refractive index fluctuations C2n and the inner scale of the turbulence l0on the M 2 factor have been analyzed quantitatively. Consequently, a new method for determining the characteristic parameters of the turbulence based on the measurement of the M 2 factor by experiments has been proposed. The results show that the laser beams with better spatial coherence property are more sensitive to the effects of turbulence, so the fundamental Gaussian beams with fully coherence can be used as the source in the measurement, and the usual instruments for measuring the M 2-factor can be adopted as the experiment equipments. It is very simple and convenient to determine the characteristic parameters of the turbulence by applying the method proposed in this paper.