The expressions of intensity distribution and coherent length of partially coherent light are obtained by using the cross spectral density function of the beam. Based on the expressions, the effects ofdifferent coherent parameters of light source and different turbulence intensity on the intensity distribution and coherent length of partially coherent light in horizontal atmosphere are numerically simulated and compared with that of completely coherent light. The results show that, in the process of free space transmission, the light intensity distribution is mainly affected by the broadening caused by diffraction, and the larger the coherent parameter of light source is, the larger the coherent length of light beam is. While in the turbulent atmosphere, the larger the coherent parameters of light source is, the smaller the influence of the intensity of turbulent atmosphere on the intensity distribution and coherent length of light is. And with the increase of turbulence intensity and propagation distance, the beam broadening effect increases, and the coherent length of the beam decreases at the same time due to the turbulence superposition effect.