The effect of δ-doping in n-type layers on crystal performance of GaN epitaxial films on Si substrates was studied by ω-scan of different crystal planes with X-ray diffraction method. The full width at half maximum (FWHM) values of the serial crystal planes of the GaN epitaxial films on Si substrates were reported. By using the lattice-rotation model, the screw and edge dislocation densities of the samples were calculated. The results showed that the screw dislocation density increased, the edge dislocation density decreased, and the total dislocation density decreased in the δ-doped GaN films. By comparing the relevant FWHM values of ω-2θ scan of δ-doped and untreated samples, it was found that the inhomogeneous strain of GaN films increased by δ-doping. In addition, LED fabricated using the δ-doped samples showed better electroluminescence performance and I-V characteristic compared with that of the untreated samples.