Based on the extended Huygens-Fresnel principle,the analytical expressions of the cross-spectral density matrix elements for random electromagnetic Gaussi an Schell-model (GSM) vortex beam propagating in biological tissues are derived a nd used to study the changes in its polarization state.The detailed investigatio n includes the influence of the structure constant of the refractive-index of biological tissu es C²_n, beam parameters (λ and σ_yy) and propagation distance z on the changes in the deg ree of polarization P,the orientation angle θ and the ellipticity ε.It is shown that the val ues of P,θ and ε are almost un changed at a length of propagation distance for the far infrared beams (λ=10μm) propagating through the biolo gical tissues.The value of ε decreases quickly for ultr aviolet beam (λ=0.325μm).With increasing the propaga tion distance z,the bigger C²_n is,the stronger the biological tissue turbulence is,the smaller the value of P is,the bigger the absolute value of θ is,and the bigger the value of ε is.When the propagation distance is sufficiently long ,the values of P,θ and ε tend to a constant in different biological tissues,respectively.Besides, the curve changes of P,θ and ε are also related to the relative magnitude between σ_yy and σ_xx.