Structure and stability of the Li-adsorbed silicene under a biaxial strain are studied by using the first-principles plane-wave pseudopotential method based on the density functional theory. Results show that Li-adsorbed silicenes keep their original configurations basically when the tensile and certain compressive strains are applied, while the silicene plane bulges towards the Li atom when a larger compressive strain is applied, and the total energy of the corresponding system becomes distinctly lower. We also calculate the phonon spectra of the silicene under various strains, and analyze the reason why the Li-adsorbed silicene is unstable under the compressive strain.