Abstract: Based on the extended Huygens-Fresnel principle and cross-spectral density matrix, the spectral degree of cross-polarization (SDCP) of partially coherent electromagnetic Gaussian-Schell model (EGSM) beams propagating in slant atmospheric turbulence was derived. The effects of light source and turbulence parameters on the SDCP of EGSM beams during slant propagation were studied. The research results indicate that the SDCP value of the entire optical field can be any non-negative value. When the coherence lengths of the light source are equal and B_ij=0, the SDCP value of the entire optical field remains unchanged. Under the same transmission conditions, the variation range of the SDCP over the entire light field increases with the increase of the zenith angle, and decreases with the increase of the internal scale.