Based on the extended Huygens-Fresnel principle,taking the random electromagnetic Gaussian Schell-model (GSM) beam as a typical example ,the anal ytical expressions of the cross-spectral density matrix elements for random electromagnetic GSM beam propagating in biological tissues a re derived,and used to study the changes above depend on the refractive index of biological tisses C²_n,beam parameters (λ,σ_yy and σ_xy) a nd propagation distance z.With increasing the C²_n,the extreme value of P will dec rease,θ and ε will increase,and the corresponding propagation distances of the extreme values will decrease.When the σ xx is fixed,the bigger absolute value of the difference between σ_xx and σ_yy will result in the quicker fluctuation of P,θ and ε along the propagation distance.Additionally,the bigger the σ_xy is,the bigger the extreme values of P,θ and ε are.Finally,the change range in the polarization states of the random electromagnetic GSM beam with the prop agation distance is superficial when propagating in biological tissues.