Bragg-Brentano几何粉末衍射中峰位、峰形和峰强的准确测量决定着粉末X射线衍射图谱的质量，同时也是正确表征材料晶体结构的前提和关键。光路中发散狭缝的尺寸会直接影响衍射峰的强度，并且不合理的发散狭缝设置会显著影响小尺寸试样的衍射峰形状。研究了发散狭缝宽度效应和长度效应对小尺寸试样衍射图谱峰背比的影响。结果表明：发散狭缝的宽度和长度限制了照射在试样上的光斑长度和宽度，光斑的宽度和长度如果大于试样的，会引起背底在低角度和高角度的显著升高，即随着发散狭缝宽度和长度的增大，衍射图谱中低角度和高角度的峰背比也会显著降低。因此，对于小尺寸试样，考虑到光斑的水平发散和垂直发散，狭缝宽度和长度的设置以小于试样的实际尺寸为宜。

The accurate measurement of peak position, peak shape and peak intensity in Bragg-Brentano geometric powder diffraction determines the quality of the XRD pattern, and is also the premise and key to correctly characterize the crystal structure of the material. The intensity of the diffraction peak will be directly affected by the size of the divergence slit in the primary beam path, and the peak shape of diffraction pattern of the sample with small size will be significantly affected by the unreasonable setting of the divergence slit. The effect of the width and length of the divergence slit on the peak-to-background (P/B) ratio in diffraction patterns of the sample with small size was studied. The results show that the width and length of the beam spot on the sample were determined by the width and length of the divergence slit. The backgrounds of diffraction patterns increased remarkably at lower or higher angle regions with the increasing width and length of the beam spot on the sample. That is to say, the P/B ratio reduced significantly with the increasing width and length of the divergence slit. Therefore, the width and length of the divergence slit were appropriate to be small than the actual size of the sample with small size due to the horizontal and vertical divergence of the spot.