Abstract: The principle of pulsed X-ray spot size measurement with lamination method was presented. The spatial resolution and output response for uniformly distributed line source of the metal-film lamination were calculated numerically. The corresponding relation between the FWHM of the response curve and the spot size was obtained. And the calculation results indicate that the metal-film lamination is not suitable for measurement of spot size less than 2 mm. Rod-pinch diode(RPD) experiments were performed on the inductive voltage adder, and the axial extent of the RPD X-ray source was measured with lamination method. Under the hypothesis of uniformly distributed line source, the axial spot size of the X-ray source was obtained, about 5.2 mm, consistent with the measuring result of the pinhole cam