Nanocomposites attaching ligand-free beta-NaYF4:Tb3+ nanoparticles (NPs) on Ag@SiO2 nanospheres were fabricated in the water solution. In the nanocomposites, the emission intensity of beta-NaYF4: Tb3+ NPs is greatly enhanced (3.9 times) by Ag@SiO2 nanospheres while the shell thickness is 35 nm, which is owing to localized surface plasmon resonance (LSPR) via both of absorption and emission matching. A finite-difference time-domain simulation is employed to demonstrate the near field distribution of LSPR and its effect on Tb3+ emission. The novel nanocomposites have wide potential applications, such as photocatalysis, false proof mark, optical sensors and solar cells.