Abstract: For getting a high quality X-ray powder diffraction pattern having higher diffraction intensity when there is only a little specimen which is not enough to spread a film in a specimen groove on a specimen plate, the preparation of a specimen plate was discussed. The discussion was based on the analysis of the change of specimen volume (width) taken part in diffraction, X-ray flux and brilliance on specimen surface, X-ray absorption by specimen in scanning. Under the condition of the width of divergence slit (DS) is fixed,for getting the largest specimen area taken part in the diffraction that the specimen size on the direction of length equals the length of the line focus in X-ray tube is better than that the specimen size on the direction of width is equal to the width of the specimen groove. But in this case the specimen volume (width) taken part in diffraction decrease with the increase of θin the range of highθ. If the slit is adjustable, the whole of the specimen in the specimen groove always take part in the diffraction. Therefore the diffraction intensity is higher. But the flux of incident X-ray is increased with the increase ofθ. If the specimen is filled in a capillary,the diffraction geometry change to Debye-Scherrer geometry or Guinier geometry which do not scanning, the flux of incident X-ray and the specimen volume (width) taken part in diffraction does not change with θ.