All-inorganic halide perovskite CsPbX3(X = Br/Cl/I)quantum dots have gained a considerable attention in the optoelectronic fields. However, the high cost and poor stability of the prepared CsPbX3 quantum dots (QDs) are inevitable challenges for their future practical applications. And the high-performance CsPbX3 QDs are always needed. Herein, a facile and low-cost synthesis scheme was adopted to prepare the CsPbBr3 QDs modified by lead bromide (PbBr2) and tetraoctylammonium bromide (TOAB) ligands at room temperature in open air. The prepared CsPbBr3 QDs exhibited a high photoluminescence quantum yield (PLQY) of 96.6% and a low amplified spontaneous emission (ASE) threshold of 12.6 µJ/cm2. Stable ASE intensity with little degradation was also realized from the CsPbBr3 QDs doped with PMMA. Furthermore, the enhanced ASE properties of the CsPbBr3 QDs-doped PMMA based on distributed feedback (DFB) substrate was achieved with a lower threshold of 3.6 µJ/cm2, which is 28.6% of that of the (PbBr2 + TOAB)-treated CsPbBr3 QDs without PMMA. This work exhibits a promising potential in the on-chip light source.