The threading dislocation density (TDD) of thick GaN films grown by hydride vapor phase epitaxy (HVPE) was estimated through counting etch pit density (EPD) and calculating full width at half maximum(FWHM)of double crystal X-Ray diffraction (DCXRD). TDD was about 108 through counting EPD, while it was about 109 through calculating the FWHMs of (0002) and (10î2). The experiment results show that the two methods are both suited to estimating the TDD of the thick HVPE-GaN films with 350um thickness. But they have some difference: EPD method is fitter in evaluating the dislocation density of the surface of thick GaN film, but FWHM method can gain the total dislocation density of thick GaN film. The method calculating the FWHMs possesses more general statistical significance.