Some related concepts of partially coherent flattened Gaussian beam (PCFGB) were introduced in this article.The propagation formula of the cross spectral density of PCFBG through ABCD optical system was derived using Huygens Fresnel diffraction integral.The transformation formula of the equivalent beam widths and Kurtosis factor of PCFGB defined by second order moment and high order moment were also derived.Using these formulas,we calculated and analyzed the propagation property of PCFGB through free space,and presented a comparison between PCFGB and FGB.The results show that PCFGB have unique propagation properties.