The strain distributions of Au/Ag and Ag/Au nanoparticles confined in the Al2O3 matrix with different core sizes are investigated by using the finite element method, respectively. The simulation results clearly indicate that the compressive strains exerted on the Au/Ag and Ag/Au nanoparticles can be induced by the Al2O3 matrix. Moreover, it can be found that the strain gradient existing in a Au/Ag nanoparticle is much larger than that in a Ag/Au nanoparticle, which could be due to the larger Young’s modulus of Au than that of Ag. With the core size increasing, the strain gradient existing in the Au/Ag nanoparticle becomes larger, while the strain gradient existing in the Ag/Au nanoparticle keeps constant. These different strain distributions may have significant influences on the structures and morphologies of the Au/Ag and Ag/Au nanoparticles, leading to the different physical properties for potential applications. The strain distributions of Au / Ag and Ag / Au nanoparticles confined in the Al2O3 matrix with different core sizes are investigated by using the finite element method, respectively. The simulation results clearly indicate that the compressive strain exerted on the Au / Ag and Ag / Au nanoparticles can be found by the Al2O3 matrix. However, it can be found that the strain gradient existing in a Au / Ag nanoparticle is much larger than that in a Ag / Au nanoparticle, which could be due to the larger Young’s modulus of Au than that of Ag. With the core size increasing, the strain gradient existing in the Au / Ag nanoparticle becomes larger, while the strain gradient existing in the Ag / Au nanoparticle keeps constant. These different strain distributions may have significant influences on the structures and morphologies of the Au / Ag and Ag / Au nanoparticles, leading to the different physical properties for potential applications.