X-ray Photoelectron Spectroscopy (XPS) is a powerful surface analysis technique that can analyze all elements except hydrogen and helium. It can analyze the surface chemical states of almost all solid and ionic liquid materials, achieving qualitative or semi-quantitative analysis of the material surface. Combined with ion etching or angle-resolved analysis, it can also -facilitate in-depth analysis and interface analysis of materials, as well as the analysis of electrical properties, such as the valence band. It is widely applied in semiconductor materials, polymer materials, catalytic materials, metallurgy, corrosion, and other fields. Solid powder material is the most common test object in XPS measurements, and its common preparation method is to sprinkle or press the powder into the tape (tape method). Generally speaking, under the same test conditions, the XPS signal of coarse solid samples is weaker, while the influence mechanism of powder particle size on XPS signals remains unclear. This study focuses on the interaction mechanism between particle size and substrate effects on XPS signals for powder samples prepared by the adhesive method, systematically investigating the impact of particle size distribution on signal intensity, peak characteristics, and elemental quantitative analysis. Using alumina (Al₂O₃) powder as a model system, XPS analysis ［wide scan and high-resolution scans of Al(2p), Si(2p), C(1s), and O(1s)］on gradient-sized samples (4.5～500 μm)，SEM morphological characterization, and the variation of the contents of elements have been studied. The results reveal a non-monotonic relationship between particle size and testing signals. With the increase of Al₂O₃ particle size (greater than 150 μm), the peak intensity of Al(2p) gradually decreases, and the half-height width gradually increases. This correlates with increased surface roughness, which affects XPS signals. When the particle size of Al₂O₃ powder is less than 13 μm, the peak intensity of Al(2p) shows a decreasing trend, while the Si(2p) signal from the substrate tape increases. It demonstrates unavoidable substrate interference. This study provides a scientific basis and theoretical guidance for optimizing XPS testing methods of solid powder samples.