Utilizing the Young′s double slits and MachZehnder interferometer，a experimental method was proposed to measure the generalized Stokes parameters of a random electromagnetic beam .After propagating through the Young′s double slits，the partially coherent beam was processed by a Mach–Zehnder interferometer consisting of apertures,quarterwave plates and polarizers.The electric crossspectral density matrix was obtained by detecting the coherence degree of interference fringe and the density of each single slit, so that the generalized Stokes parameters could be obtained .The experiment result shows that the spectral degree of coherence for copolarized cases is higher than that for crosspolaried cases. This method will help us determine the change of the polarization and coherence of the light in propagation by detecting the change of the generalized Stokes parameters.