All-inorganic cesium lead bromide (${\mathrm{CsPbBr}}_3$) perovskite quantum dots (QDs) with excellent optical properties have been regarded as good gain materials for amplified spontaneous emission (ASE). However, the poor stability as the results of the high sensitivity to heat and moisture limits their further applications. Here, we report a facile one-pot approach to synthesize ${\mathrm{CsPbBr}}_3@{\mathrm{SiO}}_2$ QDs at room temperature. Due to the effective defects passivation using ${\mathrm{SiO}}_2$, as-prepared ${\mathrm{CsPbBr}}_3@{\mathrm{SiO}}_2$ QDs present an enhanced photoluminescence quantum yield (PLQY) and chemical stability. The PLQY of ${\mathrm{CsPbBr}}_3@{\mathrm{SiO}}_2$ QDs reaches 71.6% which is higher than 46% in pure ${\mathrm{CsPbBr}}_3$ QDs. The PL intensity of ${\mathrm{CsPbBr}}_3@{\mathrm{SiO}}_2$ QDs maintains 84% while remaining 24% in pure ${\mathrm{CsPbBr}}_3$ after 80 min heating at 60°C. The ASE performance of the films is also studied under a two-photon-pumped laser. Compared with the films using pure ${\mathrm{CsPbBr}}_3$ QDs, those with as-prepared ${\mathrm{CsPbBr}}_3@{\mathrm{SiO}}_2$ QDs exhibit a reduced threshold of ASE. The work suggests that room-temperature-synthesized ${\mathrm{SiO}}_2$-coated perovskites QDs are promising candidates for laser devices.