The generalized Stokes parameters of 2D stochastic electromagnetic beams are developed to the 3D case, which can be addressed as certain linear combinations of the 3 × 3 cross-spectral density matrix in terms of the nine Gell-Mann matrices. Using the electromagnetic Gaussian Shell-model source as an example, we investigate their precise propagation laws of coherence properties and polarization properties with the help of the 3D generalized Stokes parameters. Some numerical examples and detailed comparisons of the obtained results with the 2D case are made. It is shown that 3D generalized Stokes parameters are required for the exact description of stochastic electromagnetic beams.