In this paper, a core–shell structure of Aunanoparticle@mSiO2 with controllable thickness of silica was synthesized by a modified one-pot process and then europium complex of PABI-Eu was grafted on the surface of Aunanoparticle@mSiO2 nanostructure to successfully construct the resulting Aunanoparticle@mSiO2@PABI-Eu nanocomposite. The spectroscopic result revealed that the emission intensity of the Aunanoparticle@mSiO2@PABI-Eu nanocomposite is highly dependent on the thickness of silica. The enhancement factor of 4.20 is achieved at 30 nm thickness of silica between Au nanoparticle and PABI-Eu complex.