With the rapid development of nanotechnology, various noble metal nanomaterials with multiple functions have been designed and developed, which have attracted broad research attention due to their unique physical properties and wide applications in catalysis, sensing, photothermal therapy, and surface-enhanced spectroscopy. As is well known, Localized Surface Plasmon Resonance (LSPR) response of noble metal nanomaterials including gold (Au), silver (Ag), and copper (Cu) are dependent on their type, morphology, structure, size, and dielectric function. Many attempts have been devoted to synthesizing and adjusting the morphology and dimension of noble metal nanostructures. Ag nanomaterials have good surface plasmonic properties due to their proper electronic structure and dielectric function. Unfortunately, Ag nanostructures have poor chemical stability, which seriously hinders their further applications. In contrast, Au nanoparticles (NPs) have better stability, but their catalytic activity is related to the size of NPs. Therefore, simultaneously obtaining higher-quality plasmonic and catalytic properties in single nanostructure with good chemical stability remains a hotspot issue. We report a facile wet chemical technique for fabricating AuAg alloy nanoparticles (ANPs) with high dispersibility, which integrate high stability, controllable plasmonic property, and excellent catalytic activity. A series of characterizations confirm the structure and compositional homogeneity of AuAg ANPs. Firstly, Transmission Electron Microscopy (TEM) image reveals the monodisperse nature of the as-synthesized AuAg ANPs with an average diameter of ≈ 35 nm, which indicates the purity and uniformity of the NPs. Then, Selected Area Electron Diffraction (SAED) image exhibits three clear diffraction rings that are corresponding to (111), (200), and (220), respectively, providing evidence that AuAg ANPs have multi-crystal nature. It is worth mentioning that some bright spots in the diffraction rings are found in the SAED picture, which mainly results from the (111) and (200) faces of the AuAg ANPs. This result further confirms that the AuAg ANPs belong to a polycrystalline crystal structure. Energy-dispersive X-ray (EDX) elemental mappings prove that the elements existed in the sample are uniformly distributed in the entire ANPs, and the compositions of the typical AuAg ANPs are consisted of Au and Ag. In addition, UV-visible-NIR absorption spectra of Ag NPs, Au₁Ag₃ ANPs, Au₁Ag₁ ANPs, Au₃Ag₁ ANPs, and Au NPs are detected to investigate their plasmonic properties. It is found that the surface plasmon resonance peaks of AuAg ANPs could be effectively regulated by changing the molar ratio of Au and Ag. When the content of Ag is decreased in AuAg ANPs, the surface plasmon resonance peaks of AuAg ANPs will be red-shift, in which experimental results are consistent with the theoretical ones. Finally, the catalytic performance of AuAg ANPs is also studied by choosing a model of chemical reduction of p-nitrophenol (4-NP) by using NaBH₄. It is well known that NaBH₄ individual cannot reduce 4-NP in the absence of any catalyst, which indicates the need of a catalyst for the chemical reduction of 4-NP. The reduction process is monitored by UV-Vis spectroscopy. The reaction kinetics follows pseudo first order reaction and the variations of 4-NP concentration (C_t/C₀) in the noble metal NPs with different reduction times are calculated. The corresponding results reveal that the catalytic activities of AuAg ANPs are much better than that of Au NPs and Ag NPs due to the synergistic effect between Au and Ag species at room temperature. What's more, the catalytic property of Au₃Ag₁ ANPs is the best among three kinds of ANPs. The objective of the current strategy may provide a new idea for constructing the higher-performance alloy nanostructures and developing a potential application in the treatment of aromatic nitro organic pollutants, sensing, and solar cells.